Let me throw in some ideas. I have my casting choices on the front page, but I feel like getting deeper into the roles.
The Joker, obviously, has to be an insane nutjob. He's gotta have the creepiest laugh you've ever heard, and eyes that make you want to piss yourself. It would be nice for Joker to be tall and lanky, but it's certainly not a requirement. 10-15 years ago, Robin Williams would have owned this role. But, he's a little old now, and we've got to look younger. Jason Lee would nail the terrible one-liners, the scary-as-hell laughter, and he's even got the face for it. At the same time, Jude Law is the better actor, and could get into the role just fine. Glover, while dead on in the look department, has a timid, shaky voice. The Joker needs confidence. Glover can't do that. Joker has to be over-the-top, nuts, and scary all at once. The top five for the role, in my mind, are Jude Law (Road to Perdition), Jason Lee (Dogma), Matthew Lillard (SLC Punk!), Paul Bettany (A Beautiful Mind), and Vincent Cassel (Oceans 12).
Catwoman has to personify 'sexy.' Everything about her has to scream "do me!" Angelina Jolie is literally sex in human form. She is definitely the best for it, but there are certainly other actresses who can get into such a sensuous role, but at the same time, be threatening. The top five are: Angelina Jolie (Mr. and Mrs. Smith), Rachel Weisz (The Mummy), Scarlett Johansson (Lost in Translation), Winona Ryder (The Crucible), and Kate Beckinsale (Van Helsing).
Two-Face may be the hardest role to cast. He has to have two distinct personalities. He has to be a nice, hard working fellow who believes in justice, but after being scarred, he has to become psychotic and evil. Always though, and this is the key, his two conflicting sides have to be at war with each other. In my mind, Peter Sarsgaard is the best actor to play the duel role. The top five are: Peter Sarsgaard (Shattered Glass), Leonardo DiCaprio (The Aviator), Matt Damon (The Talented Mister Ripley), Guy Pearce (Memento), and John Cusack (Identity).
The Riddler has to be a creepy, cerebral guy. I've always considered him a quiet Joker. He's creepy, cerebral, but without the over-the-top attitude. You've got to get the feeling he's always ten steps ahead. The top five are: Edward Norton (The Italian Job), Jeff Goldblum (Jurasic Park), Tim Roth (Pulp Fiction), David Hyde Pierce (Frasier), and Quentin Tarantino (From Dusk Till Dawn).
The Penguin shouldn't be a creepy sewer monster. He needs to be a smart, business-like mafia boss, who just happens to like birds - and carry around an umbrella. I doubt he could carry a movie by himself, but if he were a boss trying to fill the void left by Falcone, it could work. Everyone should call him by his name, with Penguin being an insult he can't stand. The top five choices are: Bob Hoskins (Unleashed), Kevin Pollak (The Usual Suspects), Peter Dinklage (The Station Agent), Jack Black (King Kong), and Brad Dourif (The Two Towers).
I don't feel like going in depth into many more characters, so here are the best choices for them, IMO.
Harley Quinn - Brittany Murphy (Sin City)
Poison Ivy - Kate Hudson (Almost Famous)
Bane - Nathan Jones (Troy)
Mr. Freeze - Ed Harris (The Rock)
Talia - Keira Knightley (The Jacket)
Ventriloquist - Hank Azaria (Eulogy)
Rupert Thorne - John Goodman (Beyond the Sea)
Black Mask - Ray Liotta (Narc)
Killer Croc - Vin Diesel (Knockaround Guys)
