They just did a post about this on the "Fitness" board. Not sure if you can search it, but if not, it should be within the first few pages.
*EDIT: I just posted some rap songs on the "rap songs that get you pumped" topic.
I workout to rap and hard rock, but it depenRAB on what I'm doing (weights/cardio/etc). If you list a genre, and I know of any good songs, I'll post some.