I think the most likely villian (with The Riddler out) would probably be Catwoman ... After The Dark Knight it is likely that they will need to introduce a strong female character to act as a romantic interest, and the most likely candidate is Catwoman.
I could be wrong though, I was kind of betting on The Riddler being the next main villian with Catwoman being a side villian, with the Riddler being portrayed as more of a terrorist of some sort (using his riddles to create mass panic in the city for some form of personal gain) but that doesn't appear to be the direction they're moving in.







