To whomever (sorry, can't remember) mentioned Feel Good, Inc by Gorillaz, try their song DARE. Best shake yer booty song ever!
Anyway, I just wanted to pop in here and say about the ocremix.org site, and the gendou.com sites, those both look great, and I can't wait to get home tonight and check them both out.
And just some of my favorite workout music:
DARE and a whole lot of other Gorillaz
Simple and Clean (The Planet B Remix) by Utada Hikaru
Rafiki by Zap Mama
Damn it feels good to be a gangsta by Geto Boys
Lots more, but can't think of any more right now.