WebGL Visual Debugger for Chrome
youtube.com
youtube.com
I have to say, being able to see what each drawcall is doing individually and see what each pixel goes through made me drool. I'm going to use this everyday now.
The project page is here: http://benvanik.github.com/WebGL-Inspector/
and can be downloaded here: http://github.com/benvanik/WebGL-Inspector/zipball/master