Outside of vets like Dodson, Makovksy, McCall, Benavidez, Cariaso and Pickett you have a few good prospects who could challenge in the next few years
Justin Scoggins is a great prospect. Trains at ATT with a bunch of beasts, has some of the best standup in the flyweight division already and his ground game looks great to. He can be a world champion in less than 2 years I think.
Horiguchi is a great striker but his TDD looks a bit iffy so far. I think a lot of the higher level wrestlers give him a hard time at the moment and the UFC will do the best to keep him away from them. His next fight will probably be Gaudinot
then Borg, Ortiz, Moraga, Smolka etc who have shown some decent skills
edit, just read the post about Mayday. His power would be insane at 125 and he wouldn't have to deal with the uber strong grapplers like Barao and Faber. Top 5 right away easily.