What about the third installment's villains?
It was widely believed that Two-Face would be the villain of the third installment. David Goyer, who penned Batman Begins and helped on The Dark Knight, had said that the Joker would disfigure Harvey Dent, aka Two-Face, in the third film, but we now know that Dent's disfigurement occurs in Dark Knight, and he is presumed dead by the end of the film, though the character could easily be brought back with some realistic explanation.
Asked about whether the Joker would appear in the third film (requiring the role to be recast), director Christopher Nolan stated "I don't know. I honestly have not taken a moment away from what is going on with the film now to even think about that. I don't know. I simply don't know."
Referring to how Heath Ledger's absence will affect the third film in an interview with Movie Hole, Gary Oldman stated, "Maybe we don't need the Joker. Because we'll have The Riddler."
There has been speculation on the web that the man who tried to blackmail Batman, named Mister Reese (as in "mysteries"), will turn into The Riddler, although that character is traditionally the alter ego of a man named Edward Nigma. The Mister Reese character is presented in a bumbling manner contrary to the common interpretation of the Riddler, who is one of Batman's most cunning and intelligent foes. Moreover, in one of the newspapers released with the viral marketing, there is a 'letter to the editor' that is authored by Edward Nashon, another of Riddler's alter-egos.
There is one point where Lucius Fox and Batman are discussing the new Bat-suit. Batman makes a comment about the strength of the suit, asking if it would be able to protect him from dogs. Lucius says it should protect him from "cats"--a possible reference to Catwoman.
Some fans were disappointed about The Scarecrow's small role in the film. He was, however, kept alive. This could foreshadow a return.