Underground rap is the emcees who aren't commercial, their rappers who spit their lyrics on the streets and are most likely the "realist" rappers in the game. You should listen to them more often, I'm sure you'll find them much different to the mainstream rappers like 50 Cent, because they don't talk about; money, hoes, cars and all that other materialistic, derogatory crap. Instead they express their selves by preaching about their life stories - how they were raised in the hood, or their views on certain issues in the world, could be politics or religion.

Trust me, it's much better than this fake crap you usually hear. Also, I believe Eminem's probably THE best rapper at present alongside Nas. That's it really.