Here's a rough list of what I listen to fairly frequently. Excludes some big names, but there's a pretty broad coverage in there:
Outkast, old school Common, The Roots, Rhymefest, Sole, Atmosphere, P.O.S, Zion I, Muja Messiah, Murs, Talib Kweli, cadence weapon, Jedi Mind Tricks, Eyedea & Abilities, Toki Wright, Brother Ali, The Coup, Bone Thugz N Harmony, R.A. The Rugged Man, Aesop Rock, Sage Francis, Ill Bill, Sabac, Non Phixion, Tupac, Ugly Duckling, Mac Lethal, Ludacris, Notorious B.I.G, Tupac, Nas, Army of the Pharoahs, Del tha Funkee Homosapien, Apathy, CunninLynguists, Jay-Z, P.O.S, Mobb Deep, Dan the Automator, D-12, Gang Starr, Ghostface Killah, ODB, Method Man, Hieroglyphics, MF Doom, Madlib, Sandpeople, Public Enemy, Immortal Technique, Classified, People Under the Stairs, Naughty By Nature, Run DMC, Clipse, Beastie Boys, KRS-One, Celph Titled, Ultramagnetic MCs, Reef The Lost Cauze, Little Brother, Jesse Dangerously
If you're looking for something new, in a broadly 'respectable' sense (i.e. not DMX

) then jump right in at a random name you don't recognise
