Underground:

gangstarr
afu-ra
big-l
Diggin in the crates
pete rock and cl smooth
7l and esoteric
eric b and rakim
brand nubian
del tha funkee homosapien
organized konfusion
public enemy
common
mos def and talib kweli(blackstar)
Dj hi-tek
non phixion
necro

favorite mainstream:

2pac
biggie
cypress hill
nwa
wu-tang clan