Great build, but i think you need more survivibility early-mid game. Thats one of the reasons get Rylai's first. +1 otherwise

To the AP Build:
This build is great! Most Akalis I see rush for RCS, but Akali is a good enough chaser already so i don't think that is really the best choice. When you rush the Lich Bane, HOLY SH*T. The amount of damage you can do 15 mins into the game is crazy!

About the guide its self, i love how you added the two different sections for both AD and AP. Although most people are going to be using you AP build, its good to have an alternative.

I wish i could give this more than +1.

I completly aggree with you about the masteries. Now that i think about it, Havoc isn't as great as it sounds. Hitting for 100 would mean an extra 5 damage. Yeah, thats ****ty.

Changed the masteries, and added your tip for Twilight Shroud.

Thanks for the comment, and the +!

(All incomming comments are pointed at AP build)
I'm currently working on my own Akali build, but damn! This one is somewhat the same i'm creating =P
I agree with your item choices. I'm not quite sure about masteries. Havoc is a great talent, but the points you have to spend to get it is maybe not worth it. This is dicussed alot though, as Akali is a hybrid champion. I like how you explain how and when to use abilities. Just add the fact that Twilight Shroud scares the **** out of your enemies, and can be used to avoid enemy champions from beating on your tower.

I highly recommend this guide guys, read and learn. This is multikill material!