I have played akali for the majority of my matches and every time i play her,I am shocked by how easily she can drop her foe's HP. I find her early-mid game to be most powerful, although late-game can be tremendously good as well as long as your enemies aren't allowed to completely finish their builds. With this build I often get first blood in mid lane or 1v1 top, or even a double kill first blood at solo top versus 2. being an early game character(in my opinion) I find it easy to force an enemy surrender by the 20 minute mark in about 50% of my matches. When you read through my guide, please keep in mind that everyone has there own way of playing each champ, and I'm therefore open to suggestions in the comments...just not "I play akali this way, you don't so your way is wrong" kind of comments.

Together the above runes and masteries will give you both starting passives at LV 1, allowing you to have a HUGE advantage early game due to the fact that you will have so much survivability and will be able to lane practically as long as you want. Some minor changes that you may want to make to the runes are:

1)Swap two Greater Marks of Strength(flat AD) for two Grater Marks of insight(Magic Pen)
This will give you about 2 magic pen for the price of about 2 AD and a very small amount of spell vamp(due to your passive) Either works.

2)Swap Greater Seals of Vitality(HP per LV) for Greater Seals of Evasion (dodge) Both work, I just prefer the HP per LV because I do not like to rely on chance to keep me alive.

I grab boots and 3 HP pots when first going to lane, the pots will almost garuntee that you will be able to out-sustain your opponent in lane, allowing you to either get an early gank in, or let you easily dive your enemy once you reach LV 6. The boots will help you proc your Q on your enemy early, or let you escape from early ganks like a breeze(If you even need to escape-see section on laning)

Basic akali skill priority is used.
Priority: RQEW, getting 1 point in W at LV 2
Why max in this order:

R-It is your ult, self explanitory

Q-This makes akali the assassin she is, this will do incredible damage if you PROC THE MARK.

E-A little AOE damage that can be used to heal off creep waves or neutral monsters, and can also be used when last hitting.

W-Great skill for the invisable, which is why you grab 1 point in it at the start, the defencive boost for leveling it just isn't worth it though, you are an assassin, you should be focusing damage.

Possible Spells from most recommended to least:

Flash-an overall great summoner spell, can be used for escape, chase, and ganks, often helpful when getting first blood.

Ignite-another great summoner spell, dmg and heal reduction helps get kills from first bloods, to late game team fights.

Exhaust-I find this spell about equal to ignite, a great slow and dmg reduction ability, although i find ignite better because it reduces heals, (soraka cant save , and mundo will cry) it can sometimes keep you from having to get to close to a tower to finish them off, (Q+Ignite will many times do enough dmg to a tower hugger with low HP early game) and it cant be easily escaped with flash, or a move like it.

Ghost: good for chasing and escaping, although i find flash much better because of the range you can get with flash+ult.

The rest of the spells i would not reccomend with akali, except for maybe smite if you are jungling her, in which case this is not the guide for you.

Rylais:this is a good item if you find yourself being focused down(when the enemy gets oracles and you can't kill them for whatever reason)although you should be able to kill any enemy without difficulty in team fights(even tanks) unless the enemy team has lots of AOE or the whole enemy team is hunting you down. Could also be a substitute for mejais if you are having a bad game, or void staff if your enemy isn't smart enough to get magic res.

Will of the Ancients: If you want a cheaper alternative for hextech gunblade late game, although you should end up with plenty of money if you get that far.

Boots of Mobility: I prefer the 3 speed all the time, but if you prefer the 5 speed, that is fine too.

Guardian Angel: Another good survivability item if you need one.

Merc Treads: Good for enemy teams that have lots of CC.

Quicksilver Sash: another good anti-CC item, at a very cheap price.

A test that I had in mind for a turret backdooring akali:
Stinger+rylais+Lich Bane+Rabdons+mejais+Boots of Speed
This should allow you to destroy turrets and inhibitors alike very quickly, especially if you use a spell for the lich bane passive to activate. Even though it is a backdooring akali, she would still do tons of burst damage to enemies. I myself have been unable to try this, although I was hoping if someone got the chance they could try it and post their results in the comments.

I am planning on adding more to this guide in my free time, including early, mid, and late-game sections. There will also be a Tips section. I hope by publishing this I will be able to get some early feedback and Positive comments/tips.