Veteran actor Michael Caine confirmed that the Joker will be the villain of the next Batman film, directed by Chris Nolan. And he mentioned this fact in a way that suggests the title of the next film might contain the words "The Joker," or at least have that working title.
"Now I will do something there are three pictures I want to do, small parts," Caine told TCM Online. "One [Children of Men, released September 2006] is with Alfonso Cuaron who directed Y tu Mama Tambien, I wanted to work with him and then Christopher Nolan who directed Batman is doing a smaller film called The Prestige about magicians and it's very interesting. And we're going to make The Joker next year," Caine said.
You can read the entire interview here.