I've been reppin' this guy on the bored for a good month. His mixtape is bomb and his flow is smooth. Embrace The Martian, Down N' Out and The Prayer are amazing songs. CuDi Spazzin', Man on the Moon and Maui Wowie are good aswell.
You want another good up coming rapper(s), try Charles Hamilton, Asher Roth, Wale and B.o.B. All of which were on the cover of XXL and well be the big parts of the future or rap and hip-hop. B.o.B's mixtape "Who The Fuck Is B.o.B." is pretty good aswell.
Asher Roth's mixtape "Don Cannon and DJ DRAMA present The GreenHouse Effect Vol. 1" is really fucking good. He samples all his beats, but his lyrics are incredible. Download it, it's good.
Wale has some good songs, such as "The Bmore Club Slam" and "Nike Boots". I'm not THAT in to him, but he's pretty good.
Charles Hamilton has a great song called "Brooklyn Girls". The beat is very jazzy and his flow is great.
So yea, gives this dudes a listen. They're all a bit different, but they'll be big.