This guide is to help with those interested in playing as Riven. This is directly based around making her into a glass cannon or "burst" type attack damage if you prefer to call it. I will make edits to this post if needed if I find other builds to be more useful for her and also based on your comments if you actually have a helpful or useful suggestion.
As many of you may have noticed with Riven, she is quite squishy, which makes her a focus target plus she is for the most part melee ranged only, which makes it even harder for her to fight against those other melee types that tend to be beefier and also against those that are ranged as they tend to either crowd control you or pick at you from a safe distance. This means that you probably wont be rushing the turrets most of the time. Those that are in your lane should hopefully be aware of that and not try to push too hard as it will deprive you of valuable XP and gold. With this build, I hope to achieve a fair balance of survivability and attack damage. She is average in starting health and her ability power is below average. But she has a high damage rating but not as high as others. I've been playing as Riven from release and so far I love this champion as it is the most interesting and quite different than any other champion I have tried. I hope you find this guide to be useful and informative. I do not pretend to know everything nor am I an expert, so any comments on how to change this is great and most importantly, I realize that everyone has their play style and this is mine using Riven. I owe this build to a friend of mine I met on League of Legends as they helped me with a decent build, and it seems to make sense. Have fun with it and dont be affraid to experiment :D

I had a difficult time figuring out what runes to use with this champion. You pretty much want runes that will help you early game. So I picked up 9 x Greater Mark of Desolation for my red as you will want to be able to cut through their armor rating as quickly as possible so that your attacks will do more true damage. This holds true for almost any AD based champion.
I also went with 9 x Greater Seal of Evasion in my yellows...dodge is just great cause it will help you to avoid any kind of attack, not just physical, but magical and ability based attacks as well. The boots I picked out Ninja Tabi also helps with this as well as some of the points I put into masteries...(explained later).
For my blues, I picked out 9 x Greater Glyph of Scaling Magic Resist. Most of your issues will come from crowd control and you will want good resistance throughout the entire match so geting resistance that scales with your level I feel is important.
For my quints...I chose 3 x Greater Quintessence of Health....just base health...early game you will want that survivability and also will help with beefing up your Atma's Impaler that I suggested as an item.

note: I am going to see how a build works using Great Seal of Vitality x9 and Greater Quintessence of Evasion x 3 and see which one I like better...one gives more health over all and less dodge % and the other is the reverse. I just need to see which one proves to be more useful. I forsee that the build I already posted is better early game and the other is more for late game survivability..so most likely I'll just stick with my original plan.

This is pretty basic...but I will break down each one in case anyone actually desires to read why I picked what I picked. Otherwise feel free to skip this section if you dont feel like reading all this since it is lengthy.

21/9/0

Offense
1. 3 in Deadliness and 1 in Cripple
This is basically because you do want to have a greater chance in a critical strike as they do more damage then regular attacks. Riven's abilities are based on attack damage, so you dont really need the points in Archmage's Savvy. So I made my Exhaust more useful.
2. 3 in Alacrity and 4 in Sorcery
This is because Riven's attacks are somewhat slow and to speed them up a bit is pretty nice and also because you need the points for the next tier abilities. the 4 in sorcery is nice as well cause your cool downs are reduced which will aid in getting your combos off more often.
3. 3 in Sunder
More armor penetration...for more true damage potential.
4. 3 in Brute Force
Because you will do more damage and that's what you want with Riven in this build
5. 3 in Lethality
This will allow your critical strikes to deal more damage, coupled with critical chance, this will allow you to do more damage over all more often.
6. 1 in Havoc
This will make all your attacks deal 3% more damage, and who wouldnt want that with a champion that is all about damage?

Defense
1. 3 in Resistance and 1 in Hardiness
Mainly because Magic Resist is more important for Riven as crowd control effects will be annoying for her and armor is not as much of as issue (though still important) which is what the one point in Hardiness is for. (If you are up against a heavy AD team, you may want to grab items that more closely reflect that...but really you should be downing them fairly quickly and wont need armor as much)
2. 4 in Evasion
Simply put, gives you more dodge chance...with your runes and Tabi boots...you can dodge quite often which you will need to get in close to your opponent to get those combos off.
3. 1 in Nimbleness
Once you dodge an attack, your movement speed is increased by 10% for 5 seconds which will help you with how slow Riven is and close those gaps more( or get away quicker ) since your dodge rating is fairly beefy.

That is my masteries build for this particular build of Riven..hope it helps...

This is the part that is open for change the most as I tend to change my items depending on many different aspects...which map it is, what other champions are on my team, what champions I am up against as a whole, and which ones are in my beginning lane.
The build order I mentioned is very basic and is fairly ideal for a balanced game...but as most of you know, balanced games are not always around...many times I've come up against a very heavy AP crowd control type team, and other times there are lots of stealthy champs, or lots of heavy hitters and/or early match desirables. So you must know what your own weaknesses are and how to exploit theirs or defend against what you are up against. You may find yourself with a lane mate that goes into the fray right away or maybe one that holds back at the turret. One thing can easily be said about Riven early game. You dont want to rush into anything with her...she can not withstand the heavy hitters or the ranged mages that can just pick away at your life early game. You are not a tank with this build...so dont act like one. You will most likely want to harass some and pick of those minions for last hits so you can get gold and xp as quickly as you can. Riven is more of a mid to late game champion so early on you most likely will be a target. With these items though I hope that you will find that you will have a decent amount of survival and nice damage output. The most common mistake for Riven is people spamming her Q attack. This can work in some cases, but you want to time your moves and make your combos leave you in the most ideal position for whatever you do next...it's like playing pool...position and hitting that pocket from the right angle.

I like to start off with a damage item like Long Sword and Health Potion. This will give you a little extra damage bonus and some health if you need it. Another option is to start of with Cloth Armor and 5x Health Potion, the armor will lead into the Ninja Tabi later. After that get your Boots and eventually the Tabi.
I would start building damage and health items after that...the order I put them in actually is in no particular order but I do feel that the order is fairly sound.
You will want to get to your The Brutalizer quickly for the extra damage, armor pen, and cooldown reduction. Upgrade this to Youmuu's Ghostblade later if not last. I personally want to get more health and damage next which will get you to the Phage which you will obviously want to upgrade into Frozen Mallet later..not only for the health and damage, but it will slow their attacks down which can be useful. The next item is one I change depending on the immediate need. I like to grab either Bloodthirster or Zeke's Harbinger...either way it will steal life which is good cause Riven's Broken Wings attack does proc these on hit effects. Bloodthirster will bump up your damage fairly nicely, but the Fervor will lower the armor defense of your surrounding opponents and speed up your attacks....it also helps your surrounding team mates and slowly revives their health too....but this is all situational.
Infinity Edge, this is a staple for any AD champion and is just too good to pass up, this is a must have for Riven...more damage, more crit, more kills...nuff said.
Atma's Impaler...by now you should have near 3k health and the extra added armor doesnt hurt either, but the main focus is the extra damage is deals based on your total health...just a nice addition...but if this is not your cup o tea...trade it out for something more your style.

Some optional items I've used were Sunfire Aegis for its damaging effects since you will spend most of your time near a champion..and the extra health is synergenic with the Atma's Impaler, Thornmail if you are up against a heavy AD team...they dont really like this as the more they attack you, the more damage they take, Hexdrinker + Wit's End work nicely together if you are up against a heavy AP team but I still would stick with pure damage as late game MR is not as useful as killing your opponent. Just my two cents on that one.

I am not going to get into this as much...but you want to level up your Broken Wings attack first, then Ki Burst, then Valor and of course Blade of the Exile at 6, 11, and 16.

As far as combos....without Blade of the Exile involved...you want to Valor for that quick burst and small damage reduction, then when you use your Broken Wings attack, it will reset your auto attack so you can get in one swing or two in between each use of Broken Wings. But you dont really want to stick around too long....just get in and get out...so... Valor, Broken Wings, auto attack, Ki Burst, Broken Wings, auto attack, Broken Wings, auto attack, and Valor to dash out of there and also give you a bit of damage reduction on your way out of combat...if you have Blade of the Exile...then you want to activate that first, so that your attacks will do more damage, and if they get low on health you can finish them off with the second ability of Blade of the Exile..if not...rinse and repeat or what have you depending on the turnout of your attacks and remaining health of both you and your opponent or your can mix this up depending on positioning as needed...that's what's so great about Riven...adaptability.

I changed my skill sequence...I slightly disagree with making out Vvalor early game..sorry, but I just prefer that damage first...most of the time I just use Valor to get out of the way/escape or to chase a bit...leveling it up doesnt change the distance..((I dont think anyhow...correct me if I am wrong))

I always use Flash...the second ability is up for change if you feel it necessary...some like to use Ignite or Ghost, I prefer Exhaust personally. It's just too good cause it screws them over not just for you to go after, but also will slow them down if your team mates are around and can also save them from death if need be. I just love this combo for Riven...makes her even harder to chase down or makes her a nasty chaser herself.

Pros
Good damage
Great to chase with or get away with
Flexible combos
Good mid to late game champion
Decent cool downs mid to late game

Cons
Very squishy
Focus magnet
Slow
Can run out of steam if you dont space out her attacks which makes for a sitting duck.

I guess this could be said about any champion, but especially with Riven. You want to farm for that gold and xp as much as you can when you are not out killing enemy champions...getting item advantage and level advantage is very very much needed with her as she is fairly weak early game.

All in all...I view Riven to be a very fun champion to play as..mainly because she is different than most others I've seen and tried. I feel she is pretty average...not too overpowered, but not underpowered either. She is not easy to learn, especially if you are just used to face rolling or spam clicking as some champions are like. I'd rank her in the middle for difficulty. You cant play her like most melee champions since her damage output is not as high as those like her and she doesnt have the surivability like most do as well. Get in there...do your damage, get out....she is not really one to solo with...so jump in with some team mates and utilize her combos to help defeat enemy champions.

I am currently working on a possible tank build of Riven which seems to work as long as you dont care about getting kills...with that build she becomes really hard to kill, but does not really do much for damage which I feel isnt really the point of her, but I also like to try many different option and she seems to be one that is flexible in building.

I hope you found this to be informative as well as helpful, any constructive feed back is welcome. Again..I dont claim to be an expert nor do I think that this is the only way to build Riven. I just happen to like this build and I love playing Riven. I hope she proves to be good in Dominion when it arrives.

I changed my point in Archmage's Savvy to Cripple as it only helps my summoner spell and I dont really need the AP boot.
I also changed Alacrity points to 3 and Sorcery to 4 because I feel the CDR is more important that the attack rate for Riven.
Updated skill sequence and added a not to my runes section.