The BBC has open sourced Glow, their internally developed JavaScript library.

img http://img.skitch.com/20090708-j3njets5q1g11kd5phuiy8akxq.png http://www.bbc.co.uk/glow

Check out What is Glow? for their FAQ or just grab the source right here on GitHub:

http://github.com/glow/glow1