The Knux are pretty... not good. As far as unknowns in rap go though, Micah James is god-tier (which is a shame he isn't more popular):
His only mixtape, "Agoraphobia" is free and what I'd consider a masterpiece that approximately twenty people will ever hear. Take the cool introspection of Mos Def, crank it up to eleven, and then add in some social-awareness combined with his impeccable rhyme scheme, dense yet free-flowing in it's deliverance and you have a basic image of what listening to him sounds like. Did I mention that this was from just a free mixtape?
Rap rarely gets much better than this.