Varus is the brand new AD carry and I would like to share two ways that I build him.
Please feel free to leave comments on how I can improve my guide. REMEMBER this is a guideline on how I like to play him. Try it a few times and mix the items up to your liking. Please try it out and leave a comment on how I can improve it. I want your opinion. Thank you for reading.

Credits to jhoijhoi for the template, which you can find here.

Please leave a comment if this guide helped you or how I can improve. Or Message me in game at Asgeirr and I will respond as quick as I can.

PROS Huge range Tons of cc for a carry High damage Percentage damage based on health passive damage passive attack speed increase

SPACE

CONS Squishy No real escape weak consistent damage early mana hungry

SPACE

Masteries I got 21-9-0. In offense I go the standard crit AD carry setup. In the defensive section i prefer a few points of armor or magic resist, but I mostly rely on this tree of the bonus health. The bonus health gives your carry just a little more to work with so he is not so squishy early.

The runes are nine Greater Seal of Armor- I prefer these runes to make the carry a little more tanky. These help because you will more than likely be going against an AD carry early in bot lane.

Next are 9 Greater Glyph of Magic Resist-These runes help early against the support or if you want to mid as Varus or if your opponent is has ability power moves.

For my Quintessences I use 2 Greater Quintessence of Armor and 1 Greater Quintessence of Magic Resist. These Quintessences finish off the tanky part of my builds. It makes Varus and other AD carries like Ashe, Caitlyn, or Vayne much more resilient early than most players expect.

For my marks I prefer 9 Greater Mark of Desolation- I prefer the armor penetration over the 9 attack damage you will get from having 9 Greater Mark of Attack Damage. However that is my preference use those or Greater Mark of Critical Chance if you want more of a critical chance early.

MY PREFERENCE
Heal-I always bring heal unless I have my support does. It's great for baiting people when your low and helps your team a little in fights.
Flash-I bring flash if I want the extra escape. Varus has no speed boost, or jump, or anything to get away, flash definitely help.
Exhaust-I bring this to stop someone dead in their tracks or as a way to shut down the other carry in a fight early. This combines well with Varus' cc.

OTHER GOOD CHOICES
Ignite-Most people love to bring ignite to secure a kill, definitely viable.
Ghost-Will improve Varus' movement speed and provides a long escape if you must run a long distance.
Teleport-I would only bring this if I was solo top for some reason.

BAD CHOICES
I have no use for any of the other summoner spells on Varus, but if you find one the works leave it in the comments for me.

My skill sequences are pretty much the same. How to max Varus is totally up to you. I have seen maxing his Piercing Arrow first or Blighted Quiver.
I believe either one works it just depends on the situation.
For my critical build I prefer piercing arrow first, but for the bruiser one blighted quiver works better with the attack speed early.

-Piercing Arrow - Varus readies and then fires a powerful shot that gains extra range and damage the longer he spends preparing to fire.
First Cast: Varus starts drawing back his next shot, gradually increasing its range and damage.
Second Cast: Varus fires, dealing 10/43/77/110/143 (+1.0 AD) to 15/65/115/165/215 (+1.6 AD) physical damage, reduced by 15% per enemy hit (minimum 33%).

Piercing Arrow- is your main harass. Charging it gives you ridiculous range to harass or kill a fleeing enemy. Be warned though it has 2 casts or hold it on smart cast to charge it. You can move while charging but you will walk slower. If you hold it for 4 seconds after fully charged it will fail and you will get half the mana back. Be careful if your trying to kill someone that is running. Its damage goes down significantly for every enemy it hits so take your time to aim, and if you know your going to miss just hold it for the small mana refund.I would max this first if you are with a Soraka or have blue buff all day because it takes tons of mana or going with the critical build.

Blighted Quiver - Varus' basic attacks deal bonus magic damage and apply Blight. Varus' other abilities detonate Blight, dealing magic damage based on the target's maximum health.
Passive: Varus' basic attacks deal 10/14/18/22/26 (+0.25) bonus magic damage and apply Blight for 6 seconds (stacks 3 times).
Varus' other abilities detonate Blight, dealing magic damage equal to 2/2.75/3.5/4.25/5% (+0.01%) of the target's maximum Health per stack (Max: 360 total damage vs Monsters).
This ability is much like Twitch's poison stacks however, there is no damage over time and they are not detonated by this ability. To set them off you must hit with one of your other abilities. So land some basic attacks then use Piercing Arrow or Hail of Arrows to take 15% of your opponents health.
Also this ability gives Varus passive magic damage to make up for his early low attack damage. Max this first if going with the bruiser build.

Hail of Arrows - Varus fires a hail of arrows that deal physical damage and desecrate the ground. Desecrated ground slows enemies' Movement Speed and reduces their healing and regeneration.
Varus fires a hail of arrows that deals 65/105/145/185/225 (+.6 bonus AD) physical damage and desecrates the ground for 4 seconds.
Desecrated Ground slows enemy Movement Speed by 25/30/35/40/45% and reduces healing effects by 50%.
This is pretty much a remake of Miss Fortune's Bullet Time. Varus fires a single wave of arrows that do a small to decent amount of damage, but it's effects are much more valuable.
Anything that walks through the area is slowed and loses 50% health regeneration rate and healing effects. So this skills is not only great to trap a champion, but it should be fired into the middle of the enemy team during a team fight to reduce their chances of regaining health.

Chain of Corruption (Ultimate) - Varus flings out a tendril of corruption that immobilizes the first enemy champion hit and then spreads towards nearby uninfected champions, immobilizing them too on contact.
Varus flings out a tendril of corruption that deals 150/250/350 (+1.0 ability power) and immobilizes the first enemy champion hit for 2 seconds.
The corruption then spreads towards nearby uninfected enemy champions, applying the same damage and immobilize if it reaches them.
Varus' ultimate has many uses. You can initiate when your team comes for a gank. Stop a fleeing enemy. Or pin an entire enemy team during a team fight. You must remember that this is another skill shot so take a second to aim and don't waste this amazing ult.

Living Vengeance (Passive) - On kill or assist, Varus temporarily gains Attack Speed. This bonus is larger if the enemy is a champion.
This passive is great. It helps farm minions early and gives a nice 20% bonus to attack speed to get in shots early on enemy champions. When you kill or get an assist in a team fight it makes varus super effective. You can a 40% bonus on attack speed to help finish the fight.

I have the two builds for very distinct reasons. The critical is more a regular ad carry build for a team that's not to tanky. These items are meant to max his Q's damage first for more of a sniper build. The bruiser build is for a really tank heavy team. It provides consistant damage along with shredding armor and health of the tanks. It uses is W to help lower their health. Pick whichever you think you need.

This build is used when your facing a team with a tank or a tank and off-tank. Criticals are how most AD carries do damage. These items provide nice damage as well as sustainability.
Core Items
Either Start With
-Nice boost to damage, health and that tiny life steal at early levels.
or
icon=boots of speed size=55]-The movement speed is never bad to have to run away or chase and you will also have 3 Health Potion for some sustain early.
-These are the perfect boots for Varus no matter how you build him.
-This is by far your most important item. With the boots and passive you should get damage first. This gives you a huge boost and with your W's passive magic damage you will be almost unstoppable. You should be hitting for about 500 for critical hits.
-Either get this during the process of building the Infinity Edge or right after. Life steal is a must on any carry. It will give you tons of sustain regardless of which lane you pick.
-This item will beef up your damage and make you a dominant mid game champ. Make sure to farm it to the max the extra 40 damage and 8 life steal when maxed is definitely worth it.
Situational Items
These depend on what you think you need at the time.
-This provides more movement, critical chance, and attack speed. It is a must have item for a critical build.
-Something to think about if the other team is building armor. Cheap damage and armor penetration.
-This would be for cheap magic resist,spell shield and small damage.
-Great defensive item. Health, Mana, and of course the spell shield. This may save your life in case you get focused first.
-The armor and magic resist are great, but coming back to life after being focused in a fight is great. It gives you a second chance to win the fight.
-This is the last item I get. Its damage is not important. Its the automatic slow and bonus health that make this a great way to finish your carry.
Beginner Item
-This is for someone that does not know how to maintain mana or likes using abilities a lot to do damage.

I use this type of build when I face an overall really tanky team. These items are meant to cut through armor and provide consistent damage.
Core Items
Either Start With
-Nice boost to damage, health and that tiny life steal at early levels.
or
icon=Boots of speed size=55]-The movement speed is never bad to have to run away or chase and you will also have 3 Health Potion for some sustain early.
-These are the perfect boots for Varus no matter how you build him.
madred's razor-This item gives small damage and armor, but more importantly it will help you farm early.
-This is my next choice because sustain from life steal is never a bad thing.
-Get this for cheap damage and armor penetration.
- This items gives you even more attack speed, armor, damage, and the ability to cut through tanks. Every hit does 4% of their maximum health. This will be your main damage source.
Situational Items
-Get this if you want a huge damage boost and life steal. Make sure to farm this item to its max.
-This would be for cheap magic resist,spell shield and small damage.
-Great defensive item. Health, Mana, and of course the spell shield. This may save your life in case you get focused first.
-The armor and magic resist are great, but coming back to life after being focused in a fight is great. It gives you a second chance to win the fight.
-This item should finish your build. You should be able to get through almost any amount of armor and have ridiculous attack speed.
Beginner Item
-This is for someone that does not know how to maintain mana or likes using abilities a lot to do damage.

Early game you need to FARM and by that I mean last hit to your heart's content. Do no push your lane hard unless the other team has no jungle. Just play defensive, Varus is pretty weak early game and very mana hungry so just focus on farming and maybe securing a kill or two.

Now mid game will probably start around level 8-11 depending on the speed of the game. At this point you should be pretty strong. You should have a B. F. Sword if you farmed correctly at least. If your doing good kill wise you probably will have or be close to an Infinity Edge. With your passive magic damage you will hit hard. Use your ult wisely and make sure you auto attack some stacks on before using your skills. Do not go hard in the paint. You may hit hard but your still squishy as hell and need to be with teammates.

This is where varus will shine. Regardless of which build you chose you should be carrying your team at this point. You should have a plenty of life steal and some defensive items so you can play more risky, but still stay behind your team. Let them initiate and then either focus someone or be a god with your cc. Prevent escapes and regen with your ult and hail of arrows. Worst case snipe to finish someone off. Just remember you may be a bad *** fed carry or just strong because of items, but you are not the team so don't go alone or do anything stupid.

Still Need To Test
-Testing
-Testing
-Testing
My Favorites
-If for some reason he is bot with you instead of top don't worry. Shen is a boss. Make sure to hit champs that he marks for the small health gain. And his shield is always nice if you get to low, but his taunt is where he shines. When he taunts go all out,also be ready to fire a hail of arrows to provide more cc and your ult if needed.
-Its sona what can i say,decent damage for a support, but her heal gives you ridiculous sustain for the lane phase. And who doesn't love an aoe stun from her ult.
-She is your best friend, no hard cc but the constant healing and mana supply lets you spam more if that's your type of style.
-He is another all-around helpful support. With his mix of off-tank, heal, and stun he is a good choice for a partner. And is ult can give you the extra boost to take a tower or change a fight in your favor.
-I know she is more of tank, but she is a very viable partner. The amount of stuns she has is amazing for any carry to want to lane with her. She gives you so much time to hit champions as well as escape if you must run away.
-Yet another tanky support. Alistar has not only a few cc spells but the ability to provide a small constant heal. This can be a game changer as well as his ult makes him almost invincible unless turret diving.
Decent
-She is a nice support, her shield will give you damage and help, and her ult heals, but its hard to hold a lane with her sometimes.
-Lulu has her shield, slow and ult which can totally change a fight, I don't have to much experience with her so she is decent for now.
-Lux has a small shield but her main support functions is to harass, Her slow and stun are great for this however she is useless if she can't hit her shots.
-Morgana is more of a mid champion but she is helpful. Another champion that must land skill shots and try to not farm minions with her pool to much.
-Nidalee is a great utility champion, She has damage, traps, and a heal. Her traps and heal are great but the heal does take a lot of mana so sustain may be a problem. The reason for her decent rating is nidalee tends to take a lot of kills in cougar form or with her spears which can hurt you for later gameplay.
Bad
-Everytime i have had the displeasure of being in a lane with a kayle it has not worked out well. Most kayles will not support and if they do her heal is not that good. Most will farm your minions because they want to do damage.
-He is interesting he could be good because of his ult but zilean is a champion that will take your minion kills and kills with his bombs which can hurt you for late game.

Varus is a ranged carry. That means stay behind your tanks in fights and try to kill everything that moves. Varus is great at harassing enemy champions. He can also tip the scales in a team fight pretty easily with his ult and E ability. Make sure you use all of his abilities wisely. Thank You for taking the time to read my guide please give me some feed back.

For his incomparable skill with the bow and his unquestioned sense of honor, Varus was chosen to be the warden of a sacred Ionian temple. The temple was built to contain an ancient pit of corruption so vile that Ionian Elders feared it could envelop the island in darkness. Varus prided himself on his position, as only the most exceptional Ionian warriors were selected for the role. He lived with his family in a nearby village and led a quiet life of disciplined routine until the day the forces of Noxus invaded Ionia. Their shock troops left nothing but death and desolation in their wake, and the temple lay in their path. Varus was forced to make a decision. He was bound by honor to stay and defend the temple, but without him the village's few inhabitants could offer little resistance against the oncoming war machine. Gravely, he chose to fulfill his duty as a warden. The corruption could not be allowed to escape.

His arrows sundered the troops who tried to wrest the temple from him that day. However, when he returned to his village, he found that it had been reduced to a smoldering graveyard. Remorse at the sight of his slain family gave way to overwhelming regret and then to seething hatred. He swore to slaughter every Noxian invader, but first he needed to become stronger. He turned to that which he had sacrificed everything to protect. The pit of corruption would consume him wholly, as a flame devours a wick, but its abominable power would burn within him until he was lost. This was a path from which there could be no return. With grim resolve, he condemned himself to the black flames, feeling malevolent energy bond to his skin... and with it, the promise of ruin. He left, seeking the blood of all Noxians involved with the invasion, a grisly task that eventually led him to the invasion's most infamous perpetrators in the League of Legends.

"The life of an arrow is fleeting, built of nothing but direction and intent."
- Varus, The Arrow of Retribution

5/14/12-Updated Critical Guide
Added My preferred build.
Going to add section how dealing with other champions
5/15/12
Added support champion section
Will add section on dealing with enemy champs as well as gameplay soon
5/17/12
Added a Game play section
Still going to add section for dealing with enemy supports.