I've read a few articles online here and there, interviews with Christopher Nolan. So far he's keeping the villain under wraps... There are rumors that it's going to be The Riddler, but... Those are rumors.
Gary Oldman will still be in it as Gordon. <3 I LOVE Gary Oldman. A lot. :3
As far as a villain, I think Nolan wants to keep it as something believable.... Something that fits into the story without it being to far fetched. I found an interview online with him that gave a little insight:
Christopher Nolan Speaks!