That blackalicious album is awesome. Do a search on kazaa or whatever for Quannum or Quannum MCs...its a project that DJ Shadow, Blackalicious and a few others put together a couple years back. Also someone mentioned Aesop Rock earlier...killer stuff. Def Jux has a lot of talent on their label. Some more artists worth mentioning: Atmosphere, Buck 65, Sage Francis, Company Flow, Cannibal Ox, Mr. Lif, El-P, Dr. Octagon
Specific tracks worth checking out
Sage Francis: Makeshift Patriot
Dr. Octagon: Blue Flowers
El-P: Deep Space Nine
Buck 65: The Centaur
Mr. Lif: Iron Helix
Cannibal Ox: Feeling Ignorant
Company Flow: Iron Galaxy