guys,please tell me which is the best aimbot for ut 2004 that doesnt display any code or modification on the screen or which can be easily detected by looking on my computer screen....??

you could easily have written this in one post!
It alwas depends on what preferences you have: If you want an undetectable, a free one or one with many functions,...
Many of them have settings where you can change stufflike auto aim or auto fire, thats probably how you can deal with your "binded key" 

actually most of the aimbots displays a menu on the screen .i want an aimbot which doesnt shows any thing on the screen...please tell me if u know one...

You could always buy HelioS-Framework 3.0
Undetected and tons of features (Including showing nothing on the screen)
You are not allowed to view links.
Register or Login

also it should have aimbot binded key which only aims while pressing that key and becomes free on leaving that key...exactly like shinakuma 1.7.....

like sanca said, HelioS Framework v3.0 is the most configurable/customizable aimbot for sale.

does everything you would ever want plus more.

isnt there any any such bot that is free...?

Uh no.
Due to the complications of the bot, and the time needed to create it. Most hackers want some compensation for their time spent.