Face turn: Justin Gabriel. He's got the potential of an Evan Bourne, maybe better. Women love him. He's been a high-profile guy since he came in, and he doesn't need the Nexus/Corre crutch anymore. He doesn't belong as a heel, and he shouldn't be working a heel style.
Heel turn: I don't really see anyone on either roster that is in need of a heel turn. If you're going to make me turn someone, I'd turn John Morrison. He won't get any further as a face than he is right now, with Cena and Orton ahead of him on Raw. Smackdown could use some fresh faces, but the other option is turning him, maybe putting him back with Miz and pushing them as a tandem that can bring down Cena and Orton.