I think either the Rangers or Cardinals end up with him. Rangers have plenty of hitting prospects that the Padres could use, and need a quality pitcher any way they can get one. The Cardinals would probably want another big time pitcher to go with Wainwright and Lohse, since Mulder is likely done for his career and Carpenter's in rough shape lately (not sure on his status for next season).
I could also see Cleveland getting involved. Their bats will come back healthy next year, and if they could pair Peavy with Cliff Lee, that's a good enough rotation to almost ensure a playoff berth, with the hitters they have.