developer.android.com has a nice cool look. Is it based on any known documentation tool, or is it completely custom build by google just for that site?
Just a sample of a page with multiple sidebars and table of contents widgets:
See http://developer.android.com/assets/js/docs.js and http://developer.android.com/assets/js/global-libraries-combined.js
It's just jQuery, some libraries and lots of custom programming.