Lets begin with
Two-Face shall we?

As we all know, Two-Face died in the Dark Knight. He was tackled off a building by Batman. As he plummeted to the ground, his coin landed on heads when it came into contact with the ground. I believe when it lands on heads, it meant 'Life' right? I figured that was a little hint that he was still alive. Though it was confirmed by Aaron Eckhart, that Two-Face was dead, and he was not signed on for another sequel, this is a very small possiblity that he'd return for the next film. But I feel we should move onto someone new.
Bane
I believe Bane was the first person to make Batman get his ass handed to him am I right? I think this would make it a bigger challenge for Batman. Now that he's on the run and he'll have to save the city from this raging bulky man. If you remember the boat scenes towards the end of the movie, there was a black man who asked for the remote (in the prisoner's boat), and he got alot of camera time. The movie seemed like they were setting him up as a new character. He was quite big, and I think he can pull off the role for Bane. He's already an actor, and he doesn't have to be some dipshit wrestler like John Cena or Bautista. They CAN'T act. We need the actors, not the looks. And with the great creativity of Christopher Nolan, I think he can make the story, look and feel of Bane work out. Same as he did for Scarecrow and the Joker.
The Easy Villains
Probably one of the easiest characters to fit into this film series would be Catwoman and The Riddler. Others including Deadshot, Dr. Hugo Strange, The Penguin, etc.
I know Nolan can pull off these characters without a struggle like doing Killer Croc, Mr. Freeze, and Poison Ivy.
And just to put aside all people who're tired about this batman craze, yeah, I know what I'm doing.
I'm just posting my IDEAS, not real facts on a sequel.
As far as I've heard, there is no sequel in the works.
So yeah.
Let me hear what you guys think about my ideas, and maybe show me some of your ideas and I can try to give my opinion on it.
Ciao