Most customizable gui system?
 

I want to really customize my linux but i don't know which environment is the most customizable. Any thoughts?

If you are looking for a desktop environment, then KDE is most customisable than the rest. GNOME is also good but many advanced settings cannot be changed easily. If you are looking for a window manager, then I would say go for Fluxbox, OpenBox or Blackbox because they are highly customisable.

Ok, i'll check those out..Do any of those support animation? i.e. window fades etc.

the most customizable by far is fvwm (my opinion i guess)
emacs has a mode that will syntax highlight the config file and you can do lots lots of junk with it. (spinning window fades, 70 virtual desktops)
the sky is the limit

You'll need to install xgl or aixgl to enable fancy gui effects.

Ok, thanks for the help, I'll check these out.

My opinion too, but that's kind of what you get when you write in half of the window managers functionality with the config file ;)