Speaking of The Dark Knight Returns, I know Clint Eastwood is always touted as the guy who should play him, but now at 70 (and if and when the graphic novel ever decidedly gets adapted, much older) I think that makes him a tad too old for the part. I always envisioned someone like Robert Redford as a DKR Bruce Wayne/Batman, or someone around that age bracket.
Give it a few more years and I think we could bring back Michael Keaton.
Comm Gordon - Another vote for Oldman but a younger Stacy Keach would also have been a good fit for the role.
Gary Oldman is a perfect young Jim Gordon but if they ever decided to go in an older direction, I think Stacy Keach would still work.
My dream scenario would be to see Christopher Nolan sort of pay homage to two of the four previous Batman films by bringing in Danny DeVito and Jim Carrey to play slightly toned-down versions of the Batman characters (The Penguin and The Riddler, respectively) that they portrayed in Batman Returns and Batman Forever
I can see what you're saying about Jim Carrey, although telling him to turn down the volume never really works well. But with Danny DeVito, I just can't separate him from a Penguin that is very specific to Tim Burton's universe. (And while I do very much enjoy the recent Chris Nolan films, I still have a great respect for Tim Burton's films. I think, ultimately, Batman & Gotham City don't belong in the real world. They belong inside a nightmarish gothic fantasy.)
I have such regard for the work of Tim Burton & Chris Nolan that I would probably pick a lot of their choices for the films. But for my own separate elseworlds:
Batman - Ben Browder
Barbara Gordon - Kristen Bell
Commissioner Gordon - Stacy Keach
The Joker - Mark Hamill
Ra's al-Ghul - David Warner
Harley Quinn - Nicole Sullivan
Catwoman - Angelina Jolie
Poison Ivy - Jeri Ryan
Two-Face - Robert Downey Jr.
Alfred Pennyworth - Jon Pertwee
The Riddler - My version is someone pretty young, like Adam Busch or Fran Kranz
Bane - Dwayne "The Rock" Johnson
Killer Croc - Vin Diesel
Mr. Freeze - Jason Statham
Scarecrow - Brent Spiner
The Penguin - Burgess Meredith