My ex-colleague and buddy, Luke Closs is a pretty amazing juggler. Well, he gave a presentation entitled Juggling for Geeks at the recent YAPC::NA 2007. I also happen to love juggling in my spare time (quite modestly), and so should you, it's good for the brain cells!
Check out the video for yourself, it's a pretty nice introduction to some more advanced elements of juggling, especially the pretty cool
Siteswap notation for describing tricks. Best for those that have already mastered the basic 3-ball juggling pattern, but looking for a base to learn new tricks on.