Each Nolan Batman film has had three villains technically. Yes two were dominant but still you see my point. At minimum we most likely have one more to be revealed.
Begins= Ra's, Scarecrow, Falcone
TDK=Scarecrow, Joker, Two-Face
I really would not be surprised to see three again.
TDKR=Hugo Strange and Catwoman + minor appearance by another would not shock me. Perhaps
Firefly? An arsonist for hire who it could be revealed did the torching that killed Rachel.