Common, Eminem and Outkast, though they all fell off a bit at various points (Common after Be, Eminem after The Eminem Show, and Outkast...well, after the masterpiece that was Stankonia it could never be topped really).

In terms of newer acts, holy god, Jedi Mind Tricks bitches. Immortal Technique is good too, apart from his uninformed socialist bull shoehorned into all his tracks. And can I say Kanye West? smurf you, I'm saying Kanye West.