The way I look at it, we usually have one main villain (Ra's for Batman Begins
; The Joker for The Dark Knight
), then one supporting villain (Scarecrow for Batman Begins
; Two-Face for The Dark Knight
) and then one villain representing the mob element (Carmine Falcone for Batman Begins
; Sal Maroni for The Dark Knight
So we'll probably see one main villain (possibly Hugo Strange if rumors come to be true), then one supporting villain (perhaps the female villain i.e. Catwoman or Talia the trades have been talking about) and then one villain representing the mob element (which The Penguin would be perfect for, but after Nolan's comments, it'll probably be someone like Alberto Falcone or Rupert Thorne).
That's my guess, anyway.