Trikali?

I mean maybe if you're ahead? I rather just get gunblade though.

Not too good. Only if ahead because you are a melee champ you cannot stand their autoing for too long. She also doesnt make much use of the mana or ad, so it is just a decent item.

It could work, but the reason everyone builds gunblade is that it gives more ap (which she scales much better with), and because it gives spell vamp. Akali without spell vamp is like an adc without lifesteal. Yeah you may be able to quickly kill someone, but after a few hits you're out of the fight, and being a melee champion with no reliable outs (let's be honest her shroud isn't all that great) you need a way to stay in the fight longer than half a second. Lets say that you have 100 ad and 100 ap after getting your hextech (your ap and ad will most likely be higher but easy math is best math), and let's say that all of your enemies has 50 (once again easy math). At rank 1 with these stats your e will do 130 - 50 = 80 physical damage to all opponents in its range. This combined with the 20% spell vamp from gunblade, and the approximately 22% from your passive (total of 42% spell vamp) you will gain 33.6 health back for every target you hit.

I buy TF on Akali in almost every single game and it works. Screw up Gunblade. Too much effort for "just" more spellvamp and a bit more damage. Triforce allows you to deal way more damage (Spellblade and random crits), and more usefullness overall (Movespeed, stickness, tankyness, split push potential, spellvamp - yeah, you're reading right, remember Akali's passive?)

You don't need to stack tons of spellvamp. Usually the 15~20% you can get from just passive+AD runes/masteries and itens like TF are enough. If not, buy Hextech Revolver and don't upgrade it 'till late game. Just try it, and you'll see how better your games will be. :)