Heath Ledger won a posthumous Oscar for his role as the Joker in The Dark Knight. I think he did a great job. Some people think that the role should be retired as no one could replace him. I don’t think that he did that great of a job. In fact, with the makeup, I think that he could be easily replaced by Ed Westwick. You may know him better as Chuck Bass from Gossip Girl. He was also in Son of Rambow. He has a similar build and face and could pull of the presence of the character for as much as he will be needed in any subsequent movies.
While we’re on the subject of casting, I think Bryan Dattilo who plays Lucas on Days of our Lives would be a great Dick Greyson / Nightwing. At 5’8”, he’s about the perfect height - compared to a 6' or 6'2" Batman. I just feel it needs to be put out there.
She's a bit old now, but Winona Ryder would have been a perfect match for Mai, the Psychic Girl.