IMO, Lupe should be considered one of the best of all time but he isn't at all, hence underrated.
Boldy James, MAVI, MIKE, Wiki, and Crimeapple are upcoming rappers with solid work under their names.
Your Old Droog is an old dog that never gets enough credit.
Kenny Mason - you will start hearing this name more and more in the mainstream =)
Quelle Chris is a completely independent artist who can easily compete with some of your favorites.