The Dark Knight was a huge success and one can be sure that Warner Bros is now thinking about doing Batman 3. If this hasn't been announced yet, I think it's partly because Heath Ledger, who played the Joker passed away. And also because Director Christopher Nolan wanted to have a break to do something else, namely Inception.
Update: Batman is tentatively scheduled for a release on July 20, 2012
Let's make a list of potential villains:
The sweet catwoman could show up again, but I bet Christopher Nolan would prefer a new character...
No need to present the Penguin, he's in the list, but I don't really think he will be the villain in Batman 3...
|- Mr Freeze|
Arnold Schwarzenegger played Mr Freeze, hard to erase Gubernator's performance, so we can probably take Mr Freeze out of the list.
| - Clayface|
A muddy enemy would not fare verry well on screen... Unlikely to be the next villain...
Bane is a bodybuilder on super-steroid: too stupid to be the main villain of the Dark Knight sequel!
Most likely the villain of Batman will be one of the four of the list above, that is to say: the Riddler, the Black Mask, the Ventriloquist, or Poison Ivy.
But the Joker or Two face could come back!
Christopher Nolan was quoted as saying:
So I guess it means that Robin won't show up.
According to the rumor, director Christopher Nolan's recent deal with Warner Bros for the film Inception, at least includes an agreement between the studio and the acclaimed director to helm a movie sequel to the Dark Knight. Since Inception is released in 2010, we may expect Batman 3 for 2011 or 2012.
The sooner they release Batman 3 the better!