So I've spent the past few days since Riven came out, playing her constantly to get a good feel for her. And I love her :). And you will too if you like to have a champ that plays super smoothly and can decimate someone with style! :D

NOTE: THIS GUIDE IS MEANT TO BE A HEAVY-DAMAGE BUILD! I AM NOT AIMING TO MAKE A DPS-SOAK KIND OF BUILD! THERE ARE OTHER OUT THERE FOR THAT, IF YOU WANT A LOT OF KILLING POWER, AND KIND OF A GLASS-CANNON TYPE DEAL: THEN THIS IS IT!

Pros:
+Plays like a dream
+Solid skills
+Sweet Ult
+Good damage
+Fights with a broken sword. COMON
+Good farmer
+Doesn't use mana
+Can get away easy or chase

Cons:
+Very squishy
+People will assume you suck, considering she just came out
+Takes a little getting used to

For masteries I went 22/8/0. Riven needs the extra Offensive power, but also could use a little bit of defense, because of her tendency to die easily.

-->-->-->-->-->
: Berserkers greaves are a nice little addon for Riven. She gets the extra attack speed, which will complement the black cleaver purchase you make shortly thereafter :).
: The Black Cleaver is a REALLY solid item for Riven early on. It adds extra attack speed, damage, and also reduces the opponent's armor. AND it stacks. This is a must have for Riven. However, if you aren't doing so hot, grab a Wriggle's Lantern for some extra armor and leech.
: Phantom Dancer is a good buy as well. Increased attack speed, crit chance, and movement speed will give you enough staying power and the ability to kill on sight :).
: Infinity edge is an awesome addition to her damage output. It'll add some AD, as well as some needed crit potential. You may not get this in an actual game, but it is still a good buy :)
: Since Riven is pretty squishy, GA is not a bad idea. Some extra armor and the ability to regen is a nice bonus. By this point you probably won't need anything past the infinity edge, because the game will be over, but grab this if it drags on.
: This just adds insult to injury. You will probably NEVER reach this point, but if you do, you already have the killing power, so grab some more defense. NOTE: IF YOU WANT MORE DAMAGE, GRAB ANOTHER INFINITY EDGE INSTEAD OF THIS

: Runic blade is the PERFECT complement to your Broken Wings. It charges itself every time you use an ability, and yes, every activation of Broken Wings adds to this stack. ALWAYS attack in-between uses of Broken Wings, so that you use your charges and deal tons of extra damage.
: I've seen a lot of people just spam this move without attacking in-between. MISTAKE. This is a 3-part combo that you can activate while using basic attacks as well. Use this to get away too, because it rushes Riven forward a little bit. And as I explained, always use basic attacks while using this move. I prefer maxing this out before valor, but not before Ki Burst, due to the nice burst damage potential.
: Ki Burst is the skill you want to max out first. It does a nice chunk of damage, and always stuns the target for a little while. I usually throw this in in the middle of a Broken Wings combo, generally after the first or second hit, then I activate Blade of the Exile and finish them off.
: Valor is an awesome skill. It dashes you away, and puts a shield around you. This skill is great for dodging, chasing, and getting away. Valor + Broken Wings makes Riven one of the most mobile characters in the game.
: This ultimate is AWESOME! It increases your range of your attacks and abilities upon activation. Additionally, you can use Wind Slash to finish off opponents after a combo, as explained above. Don't waste this ult, only use it when you've already damage someone in the middle of a combo.

--


Flash: Flash is a MUST HAVE for Riven. Added to her mobility, this skill will allow you to get away easily, or chase a foe that would have gotten away otherwise. Don't use it randomly, however, only use it if you KNOW you can get the kill, or you're SURE you're going to die.

Exhaust: Exhaust is an amazing spell and it will get you a LOT of kills you wouldn't have gotten in most situations. It slows them, and they're dead. It's that simple.

Alternatives

: Teleport is okay. It gets you to your lane faster, which is nice, or tele in to help a teammate and get the kill.
: I prefer exhaust or flash to ghost, but ghost is definitely an option. Most of the time, though, I find myself getting exhausted while using ghost, then it just became useless. But nonetheless, that will not happen in all situations. So still a good alternative.
: Some people like to use heal, personally, I'd prefer the chasing/running power. But, to each their own. :)

DO NOT USE

Early Game

For early game, grab your Doran's Blade (Or boots and potions, if you prefer) and take either the bottom or top lane. Preferably with someone who can stun, has a lot of CC, or is a tank. Riven can kill EASILY with a little backup early game. I've had multiple instances where I've killed two people before minions even spawn. Yes, they might have been terrible, but still :). Stick a point into Broken Wings first, it will be a good farming tool, and harassing tool. If they get close, make them pay. Broken Wings - AA - Broken Wings - AA - Ki Burst - Broken Wings - AA will be your main combo at this point in the game, and it will do a nice chunk of damage.

Mid Game

By now you should at least have The Black Cleaver, if not Zeal too. Now, you have a lot of slaying power :). Getting Black Cleaver early on will dominate the lanes. You should also have Blade of the Exile, so USE IT! Your combo now should be: Broken Wings - AA - Broken Wings - AA - Ki Burst - AA - Broken Wings - Blade of the Exile - AA - Valor - AA - Ki Burst - Wind Slash. Yes, I know this combo seems rather long, but while you're playing, it will come naturally if you practice it. :)

Late Game

By Late Game, depending on how you're doing, you may want to grab the Guardian Angel. If not, go ahead and snag more damage with infinity edge. Sheen is an AMAZING addition to Riven, so grab that if nothing else. By late game, you may want to grab more armor, or damage. Preferably the armor, because the black cleaver - phantom dancer - infinity edge combo will give you a pretty good amount, and now, you just need to live.

9/16/11: Released the Guide
9/16/11: Added two sections
9/16/11: Shifted out Tri-force