I think everyone has a secret desire that he plays in Seattle. I know I do.
also, another sleeper I think might be Paul Davis, unless I screwed up and he's not in the draft this year. But anyway, he may not have the ideal NBA body, but I can see him being a late pick that ends up contributing
I think James White has the potential to become a good player (maybe a better version of Ruben Patterson), although I doubt he'll be a star like Redd or Arenas. Of course, he's supposedly moving into the 1st round, so if that's the case, he doesn't really fit your question.
Good call on Leon Powe. If he stays healthy, I can see him getting 12 and 10 regularly in the NBA. He has range up to about 15 feet and he has tremendous upper body strength to bang inside. He also is very explosive and has intense athleticism. I can see him being a Larry Johnson with less range.