The expected villain for the 3rd installment of the Batman movies is The Riddler. Nothing is set in stone, but clues lead many to believe that The Riddler will be Batman's next victim. There has been no release date or timetable for when shooting of the film will begin. It most likely won't be for awhile as Chris Nolan likes to take his time in between making movies (3 year break between Batman Begins and Dark Knight) and he is currently filming a movie called Inception.
I think Nolan taking his time to create the 3rd movie will benefit the viewers because he will be able to make a sequel just as, if not better and thrilling as The Dark Knight.
As for Robin, there is little chance he will be featured in the upcoming movie as Christian Bale enjoys the spotlight and will "refuse to go to work" if he is added.