Bruce Wayne / Batman - Joe Manganiello (True Blood, Spider-Man) If the franchise continues, I don't want to watch another young Bruce Wayne grappling with his choice to become Batman. I want a mature Batman who's been at the game for a while, and Manganiello is perfect to embody the older, worn down but still fighting, hero.
Alfred - John Cleese (Monty Python, Rat Race) I know he's too old, and semi-retired from acting, but dammit, he would have been perfect.
If you have to have someone younger.. Bill Nighy.
Dick Grayson - Reece Thompson (Assassination of a High School President, Rocket Science) Very talented young actor who can easily handle Grayson's mourning, rage, sense of humor, and, eventually, transformation into Nightwing.
Commissioner Gordon - Dennis Quaid (Vantage Point, Day After Tomorrow) Assuming Gordon is already Commissioner, I could see Quaid as someone beaten down by Gotham, but still hopeful for a better future.
Joker - Bill Hader (SNL, Paul) Fantastic comedian with great range of voices and facial expressions. He's tall, lanky, and can easily be scary if given the opportunity.
Penguin - Timothy Spall (Harry Potter, The King's Speech) There's no one else.
Riddler - Michael Sheen (Frost/Nixon, Underworld) Such a great actor who can easily be both cerebral and creepy.
Mr. Freeze - Ed Harris (The Rock, Gone Baby Gone) Great actor who can make Freeze both tragic and frightening. Plus, he's got that steely, cold blue eyes.
Victor Zsaz - John Hawkes (Identity, Winter's Bone) Underrated actor who can really make Zsaz terrifying, not just a small obstacle or henchman.