Welcome to my Akali guide. This is a different build then the ones you might be used seeing (AP Akali). I find this one to be more consistent, and the damage output to be fairly better, with a huge burst. Also, it's harder to counter you, since you're hitting like a truck in both AP and AD. Sit back, relax, and enjoy!

ARP Marks: Allows you to dish out alot of damage vs squishies early game, and facilitates your last hit.

HP/p level Seals: Makes you more durable. Feel free to take dodge seals if you like, just make sure to spec 21-9-0, taking the dodge masteries, obviously.

AP/p level Glyphs: Allows you to proc your passive at level together with the Quintessences, and doesn't make your AP fall throught the game.

Flat AP Quintessences: Solid AP early game, and makes you proc your passive at level 3, nuff said.

21-0-9 is, in my opinion, with my runes, the best you can get. You're supposed to be mid, and most midders have the Exp. gain talent, and this will allow you to keep up levels with them. I don't think I need to explain the Offensive Masteries.

Note: Take 21-9-0 if you have dodge seals, obviously.

Open with a Doran's Blade. If you're good with Akali, you'll First Blood/kill your opponent around level 4-5, and if you last hit decently, you'll have around 800+ gold when you do. I suggest you go base after farming the coming minion wave, if your health allows you, don't overextend. Buy Boots of Speed and an Amplifying Tome. Some Health pots help too. From there, finish your Hextech Revolver, Sheen, Brutalizer - these are the core items. I normally go for Boots of Swiftness. If I'm with my premade, Boots of Mobility for farming/ganking with ease. Heavy CC team? Mercury Treads. After these 4 items, finish Youmuu's Ghostblade, followed by Hextech Gunblade. If you feel you're too squishy, take Phage. Now you have 3 choices: Finish Trinity Force, make Infinity or make Rabaddon's.
I don't recommend you finish Trinity right away.
Infinity > if the opponent team has more MR than Armor.
Rabaddon's > if the opponent team has more Armor than MR.
Now finish Trinity. Start buying Elixir of Fortitude/Brilliance from level 14 on.

MotA > 1,8,10,12,13
TW > 2,14,15,17,18
CS > 3,4,5,7,9
SD > 6,12,16

Here I'll explain why I choose these summoner spells.

Exhaust: Makes you basically unbeatable on a 1v1, and allows you your first kill in lane VERY early due to your huge damage output.

Flash: Great escaping tool, chasing ability. Together with TW, you can escape almost every situation/gank, if you're good.

Other choices:
Ignite > better if you're AP, to help you dish out damage, not needed.
Heal > I just hate this summoner spell, simply because I died so many times in a 1v1 'cause of it. Don't take it, please.
Clarity > lolwut?
Ghost > Can be taken instead of Flash, matter of preference.
Rally > Again, lolwut?
Clairvoyance > Let a support take it, you're a carry.
Cleanse > It's good, yes, but I stopped using it 'cause of Flash. Again, matter of preference.
Fortify > *sigh*
Revive > You're not supposed to die, so, yeah.
Teleport > Can be taken to solo farm, gank if you teleport to a ward, but I don't like it.~
Smite > You're not a jungler.

«Pros»

*Heavy burst damage
*Consistent damage in a teamfight
*Not so squishy
*Great escape/chase mecanisms
*Farms like crazy
*Massive Spellvamp/Lifesteal
*Hard to counter since you're Hybrid

«Cons»

*Dies easilly if focused
*Disables screw you over (stun,fear,silence,shackle,etc)

I don't find her to have many cons. ^^ Please say if you find any, though.

Hope you enjoyed, and it's detailed enough, if not, I'm sorry, it's my first guide. I recently started using this build, and I find it funnier than the regular AP build, and it's cheap to buy it, both rune, and itemwise. I find it more effective also. Remember, TRY to take mid, and draw First Blood, you'll have a huge experience edge, money, and you will destroy his morale. (oh no, I died to an Akali, she's gonna get feeded *surrender at 20*) Harrassing with Akali?

Q > R > Mellee hit > E

Repeat until kill, but remember, don't overextend. You're squishy early game, care for ganks. Once you reach level 6, start ganking lanes. It'll help your team, and if you manage to grab a kill, it's awesome. From level 8+ or when you get Revolver, get Blue and Red Buffs, and keep farming/ganking.

NOTE: This is not a guide for begginer Akalis. Build your regular AP build if you're not so good with her for better results.

For all you good Akalis, I hope you like it, make it, and own like hell! ^^
Feel free to comment, but please, don't be trolls. <3