So Riven has been out for awhile now and it seems that people have varying ideas on how to properly build her. There are a great many options but from day 1 I have disagreed with Phreak and the Champion spotlight and have had exceedingly good luck with this build. She is a powerful champ and I feel like she is one of the more balanced champs they have brought out in recent history.

For Runes I likeand
Now there are many options that would work well. Armor Pen, Flat Armor, Flat health are all solid choices for quints. Armor, Magic Resist and Cool down reduction all work well for Glyphs. Armor Pen, Critical chance are both decent ways to go with Marks and Armor, Crit chance are solid choices for Seals.
Really when it comes to Runes it really depends on what you like.

I always start with http://edge4.mobafire.com/images/ability/riven-broken-wings.png followed by http://edge4.mobafire.com/images/ability/riven-ki-burst.png and http://edge4.mobafire.com/images/ability/riven-valor.png From there it is sort of up to you. Maxing http://edge4.mobafire.com/images/ability/riven-broken-wings.png is never a bad idea but if you use this build I suggest you spread the points out because lving up http://edge4.mobafire.com/images/ability/riven-ki-burst.png and http://edge4.mobafire.com/images/ability/riven-valor.png lowers their cool downs and allows you to use them more and proc Sheen more often.

So if you have spent time playing Riven you know that without the correct laning partner or against certain champions her early levels can be kinda tough because she is one of those in your face type of champs, of course she can also be very strong early on as well. Either way I like to start with a http://edge4.mobafire.com/images/item/dorans-blade.gif to help stay in lane and earn gold. http://edge4.mobafire.com/images/item/ionian-boots-of-lucidity.gif are great for the cool downs making her skills very spammable but keep in mind if the enemy team has a lot of CC are almost always the way to go. A http://edge4.mobafire.com/images/item/wriggles-lantern.gif will give you some good early sustainability with the Armor and Life steal as well as the free sight ward which most people seem to neglect in games.
I always try to get a http://edge4.mobafire.com/images/item/sheen.gif early in the game because this 1 item synergizes with all of Riven's skills perfectly. It does require you to be mildly patient and use her Q smartly.
Example -
Q - Auto Attack - Q - Auto Attack - Q - Auto Attack - W - Auto Attack - E - Auto Attack.
So on and so forth. Of course different situations call for different combinations but always allow for an auto attack between skills to really maximize your dmg output.

Mid game I try to pick up http://edge4.mobafire.com/images/item/warmogs-armor.gif and http://edge4.mobafire.com/images/item/atmas-impaler.gif as soon as possible and finish up my http://edge4.mobafire.com/images/item/trinity-force.gif With the trinity her dmg output is good enough to let you become more tanky so you can stay in fights longer and still put out a good amount of dps. Follow that up with an http://edge4.mobafire.com/images/item/infinity-edge.gif and if you get that far trade in your
http://edge4.mobafire.com/images/item/wriggles-lantern.gif for a http://edge4.mobafire.com/images/item/the-bloodthirster.gif and you should be rocking some very brutal 1300+ dmg crits as well as fantastic survivability.