Depends on the style you're looking for but here's a list of underground that I'm assuming you're looking for,

One Be Lo
Ohmega Whatts
Binary Star
Souls of Mischief
Lightheaded
Akira
Edan
The Non-Prophets
Murs
Grayskull
Brother Ali
Blueprint
Mr. Lif
Hieroglyphics
Digable Planets
Zion I
The Perceptionists
The Anti-pop Consortium
Foreign Exchange
Pharcyde
Othello
Platinum Pied Pipers
Akrobatik
People Under the Stairs
Mr. Brady
Swollen Members
Abstract Rude

These are all more traditionalist, battle emcee, mainstream but not styled artists. If you want more abstract and experimental artists just ask and I can roll out that list too. I can give you more like what I just gave you aswell if you want that too.