WTF no one mentioned Atmosphere or Eyedea. LoL.
Personally, I despise Aesop Rock. The rest of Def Jux is decent.
Maybe pick up the Weathermen mixtape, "Weatherproof." The Weathermen line-up is decent:
El-P, Cage, Copywrite and Vast Aire are probably their best known members but this kid Breeze Brewin isn't that bad, and Jakki da Motamouth is like an auxilary member.
Eh. Have fun with the underground, but don't stay there. There's a reason some emcees are still underground.