There's a place on U street called Behemian Caverns, they have a free jam session hosted by The Young Lions (Allyn Johnson on keys, Chris Fon on double bass, and Quincy Phillips on drums) that's just killin'. It's really late though, but if you can check it out, you should. I think it's on Saturday night. Also, Utopia (also on U street) has live music every weekend night, my friend plays sax there sometimes. Twins and the place right next to it (also on U street) also have pretty good live music, but sometimes it's just this pissy old black dude who kinda sucks.
The Dude