Over the past 3 years, i have been exploring this genre. Its as vast as the genres of metal that i grew up on, and cover just as much ground... from political stance to social issues, etc etc.
These are a couple notable artists for me, aside from the guys that initial got the ball rolling for me (Sage Francis, Atmosphere, Murs, Sole, Doseone... etc)
Afu-Ra didn't really make it prime time, but his collaborations with DJ Premier and Guru would get any hip-hop head to give him a shot.
Lastly, Masta Ace has been hard at work since the early 90's, and is well respected in the underground. Give him a shot. All of his tracks have a buzz and a unique flow.
Thanks for reading!