Welcome to my twitch build! I will gladly admit i'm not lvl 30 yet, but this build has given me some insane advantage over enemies, provided I can play defensively enough at the start.
If you think something needs to be changed in the build, feel free to let me know! I have every intention of tweaking the build as I go.

Expect end results to be around 70% crit chance, around 50% life drain, and insane movement speed.

Greater Quntessence of Furor: 13.38% additional crit damage.
Greater Mark of Furor: 20.07 additional crit damage.
Greater Seal of Furor: 7.02 additional crit damage.
Greater Glyph of Furor: 5.04 additional crit damage.

Total bonus crit damage = 45.81%
(Attack Dmg x2) w/o Infinity Edge
(Attack Dmg x2.5) w/ Infinity Edge

With Infinity Edge, this puts you at 3x dmg on crits.

Priority: Spray and Pray, Ambush, Expunge, Debilitating Poison.
Exception: Start with Ambush, Debilitating Poison, Expunge, then follow priority for the rest.

This is my standard for this build. Granted, if you're not lvl 30, place majority in attack bonus for now. Twitch will be needing the utility over defensive because you don't want to be taking damage for long anyway! It's hit and run, and let me be crystal clear on the RUN part! The added exp boost and mana regen is a ton of help. Be sure to grab both the blue and red buffs when you can. Red adds a slowing effect, blue helps with manapool recovery, and lets you escape faster with cooldown reduction.

1) Brawler's Gloves: By starting with this item, you boost your crit chance to 10%, giving you a better chance to kill not just minions, but get the first blood.
2) Vampiric Scepter: Fortunately, you pick up a good chunk of healing with this!
3) Executioner's Blade: More crit, more life steal, and damage over time!
4) Last Whisper: Great for those who stack armor...
5) Zeal: As insane as it sounds, grab this first! Crit chance, attack speed, and movement bonus.
6) Boots of Mobility: You can pick these up now, or wait for Phantom Dancer
7) Infinity Edge: Now you are doing 3x crit damage, and crit should be in the high 70% range.
8) The Bloodthirster: Gives you a little more damage, and life drain.

If you feel an item does better, please provide why when you post the suggestion. The end lineup is this: Avarice Blade, Phantom Dancer, Boots of Mobility, Infinity Edge, The Bloodthirster, and Youmuu's Ghostblade.

Potential change: Instead of a +5 from boots of mobility, if you prefer a constant boost, go for swiftness boots instead.

Clarity: Very helpful little tool for when you run out of mana, and it will happen. I recommend this in high priority!
Heal: Again very useful for getting the first kill. Doesn't do nearly enough mid or late game, but sometimes it is the difference between 2 kills and 3 when people try to ghank you.

Exhaust: ... Pointless because you will be able to outrun them 90% of the time anyway, and when you cant, Debilitating Poison fills the gap.
Ignite/Smite: Woln't do enough good ever. Aside, executioner's blade fills in for ignite.
Clairvoyance: Nice, but also fairly pointless. One kill at a time, and the two suggested are a lot more useful.
Teleport/Flash: I guess this could be useful for a quick escape/ghanking, but normally you can outrun people, so just go stealth, and have fun!
Rally/Promote: equally useless, your mobility would put you out of range way too fast.
Fortify/Revive: I can't imagine it will be hard to stay alive. Let a support carry Fortify!

4/30/2011: Decided to replace Avarice Blade>Youmuu's Ghostblade with Last Whisper. Decision based on need for armor pen vs enemy champions. Minions were taking 600+ dmg, champions who stacked armor were taking 150~170. Considering stacking a second, and replacing executioners calling with The Bloodfeeder after second. Will test later.

5/2/2011: Still leaving The Bloodfeeder on the build, but late game if you are completely dominating, you should consider another phantom dancer. Crit rate becomes 100%, you attack faster, and have around 470~500 movement speed, easily.