I always thought Alec Baldwin, back in the 80's, would have been an ideal Bruce Wayne/Batman.
Alan Rickman, from any era however maybe the Die Hard
timeframe would be best, was always my ideal Alfred Pennyworth.
Gary Oldman IS Gordon to me. I'd be hard pressed to see someone portray him better.
Sydney Poitier as Lucius Fox, from a few decades back.
A young River Phoenix as Dick Grayson/Robin.
Robin Williams, from any era, as The Riddler. Willem Dafoe, from the late 90's, early 00's, as The Joker.
To me Liev Schrieber was always born to play Harvey Dent/Two-Face.
James Gandolfini as Detective Bullock. Philip Seymour Hoffman as The Penguin.
Marlon Brando (The Godfather
era) as Carmine "The Roman" Falcone.
On second thought, William H. Macy would make a great seasoned Comissioner Gordon.