12/23/2012 - Guide released.
1/11/2013 - Replaced Hydra with Blade of the Ruined King, rearranged purchase orders, added Guardian Angel to the end of each build.

Vi is an amazing champion who excels in pinpointing and singling out opponents or chasing them down if they think they can get away (they can't). She is by far one of the best initiators out so far and, if built right, she can prove to be an integral part of any team. Whether it's assisting your team to get them fed or feeding on the enemy team yourself, Vi is incredibly fun and easy to play, while providing a world of versatility on the Fields of Justice.

*KEEP IN MIND!*
Vi really shines as an actual killer mid to late game. Early on, just focus on helping your team secure kills and getting as farmed up as possible (very easy with her AOE madness). Vi is a champion of early patience and later foolhardy recklessness (within bounds, of course). I've had several successful games with her so far with this build and think the rest of you who have a similar play style will have fun with it.

With this build, you can't be afraid to initiate team fights, but you also still have to play smart. I've had several consecutive wins with this build on Vi both on 5v5 and 3v3. Hopefully I can put some more sources up later on.

As mentioned in the notes, though a great chaser with her abilities, she has absolutely nothing when it comes to basic speed. This fact, combined with her great ability as a bruiser, really requires the slow from Frozen Mallet. I don't go with Trinity Force because I like the 'sure thing' slow rather than just the chance to slow.

Combined with the attack speed, critical strike, and movement speed from Statikk Shiv makes Vi an uber damage dealer. If you farm and/or gank correctly, you should have this build anywhere from 20-35 minutes in, give or take. Few champions can go toe-to-toe with you at this point. I don't go Phantom Dancer simply because you don't get the added effect of the GP10 item before the full build and the simple fact that Statikk Shiv is cheaper. Feel free to trade these out later on if you'd like. The unit ignore on PD will help out with chasing as well, so either are good picks.

In the end-game, get what you want. I prefer Blade of the Ruined King fairly early because it simply adds a ridiculous amount of health destruction. At level 18, you'll be doing roughly 20-25% of their health with every 3rd hit (cumulative). Black Cleaver will leave your enemies with no armor whatsoever, making them even more pwnable. Build how you like, I usually don't need to get that far anyway before people start surrendering. More attack speed never hurts either.

I've heard Icebourn Gauntlet is a good choice as well, I simply disagree because Frozen Mallet is all you really need for slows since your bread and butter comes from Denting Blows and auto attacks. IMO, you could be putting your money to much better use.

The runes are pretty basic, both taking attack speed glyphs to help get that Denting Blows passive going ASAP. Armor pen for the jungle is so that more of your damage gets through, though it can be replaced with simple flat AD as in the Top Lane build. Basic armor seals and, of course, your AD quints.

The Masteries are pretty straight forward as well, taking the full AD tree in offense for as much damage as possible, with some added tankiness along with in defense. It's worked well for me so far, but feel free to experiment.

I explain this a bit in the skill notes, but just for good measure, I like taking Denting Blows in the jungle because of it's passive, and Relentless Force for harass in the top lane.

Relentless Force is essential to max out first since it has great burst damage and can help secure early kills, as well as give you an edge in later team fights from the AOE damage.

Denting Blows is next since at around the time that is maxed out, you'll have some more attack speed build to simply shred the enemy armor and health.

Vault Breaker is usually just for some utility; a get in and get out kind of a thing. The cooldown is pretty lengthy and it wont do much unless fully charged in a fight, so it's better to leave it till last IMO.

Try to get either your jungle or yourself fed in Top lane, but don't be upset or surprised if the kills don't come pouring in at the very beginning. Stay fairly passive, since her slow movement speed makes it difficult to get out of sticky situations if you're ever ganked. God forbid you use Vault Breaker and their jungler knows enough to stand in front of you to stop it. Get farmed up and don't feed your lane while helping your jungler secure kills with you, or simply roaming to help the rest of the team. You'll shine later on as long as your team knows not to focus the enemy tank while their main damage dealers pick you off before you can get an ability out.

While jungling, try and get your team to bait the enemy into pursuing them, charging your Vault Breaker as you approach the river bush (or wherever) in order to knock the enemy champions close to them, making escape much harder. Burst quickly and pray they can land a kill since chasing is not a Vi-able option without Frozen Mallet or the Red Buff.

In any situation, make sure to save your ultimate for either a single kill, or their carry at the start of the team fight so the rest of your team can catch up and secure the kill quickly before turning to the rest of the team. Aside from Vault Breakers brief knockback (despite the long charge time and abrupt end on hitting ANY enemy champion), you have no more CC to use on keeping damage off anyone, so focus your FM on the next champion (usually the AP carry) while ignoring the tanks in order to minimize the damage taken to your own carries. Vi will be able to clean up just about anyone else left over, so don't get discouraged or back out if your ADC takes a dive. Vi got dis!

The Champion Spotlight does a pretty good job of explaining this, but if you haven't seen it, line as many minions (jungle camps) up as possible, shoot through with Vault Breaker, then turn and clean up with Relentless Force. Farm madness. Also be sure to use Excessive force right after an autoattack to get another stack towards Denting Blows along with faster damage output.

I stole it from the Champion Spotlight and it works just fine. Thanks Phreak! :P

Pros:

1) Great chaser after Frozen Mallet.
2) Takes enemy tanks down in no time.
3) Sacrifices little damage when building tanky (as long as there's additional attack speed).
4) Very easy and simple to use.
5) Great initiator.
6) Trollface dat Ezreal Essence Flux.
7) Great AOE.

Cons:

1) Slow
2) Escaping impossible unless there's a clean line of sight ahead of you.
3) Vault Breaker goes on CD if CCed out of it.

This is pretty much it for now. If anyone has questions or additions that I missed, please let me know. Have fun playing and let me know how the build works out for you!