I've got like 5,000 songs on my iPod, not including podcasts of new music from Audiofile and Better Propoganda.
A few themes emerge upon closer inspection:
90s hip hop
90s alternative soul (I classify this broadly: from Erykah Badu to Ben Harper)
Late 90s-00s ambient music (St. Germain, Labwaste, Rysoop)
Zepplin-inspired rock (Audioslave, Queens of the Stone Age, Living Coulor, and of course Led Zepplin)
Alternative (TV on the Radio, Handsome Boy...