I'd nominate Tommy Sanders from Beaumont, TX. He doesn't play anymore from what I hear, but he's beaten more than his fair share of champions. Even John Hager Jr, who everyone keeps praising in this thread, has utmost respect for Tommy's game. One of Tommy's most notable victims for the cash was perhaps one of the three or four greatest 9-ball players of the past two decades -- Earl Strickland.
I'd also nomiate Henry Busheer, aka "Patch Eye", from Philadelphia. No one who sees this old, decrepit-looking 70-something black guy with one eye would think that he can play. Well, even Grady said that he couldn't give him more than a ball or two at one pocket back in Patch Eye's prime, and he can still play -- he was third or fourth at DCC One Pocket in 2000.