The Joker - Lately I've been loving the manips of the Paul Bettany, but yet to see any of his films. He has the height (6'3"). But on acting skills, I'd like to see what Johnny Depp would do with the character. Sure he's only 5'10, but that can be inhanced. But I think no matter the manip of Conrad Veidt which has been going around will be used as the inspiration of design for The Joker, just like the comics. And if The Joker is going to be dressed in style, as he should, no purple. Just the black tuxedo. I like that Alex Ross approach.
Harvey Dent/Two Face - This has been around for a while. Liev Schreiber. The important thing about Dentis that he is the Appolo. He's a young, good looking guy with everything going for him. Then its destroyed and he goes nuts. Schreiber can play Dent and he's a good actor, he can tap into Two Face.
Penguin - I approach this as one of the minor characters for the films. A mob boss at the iceberg lounge with taste for tuxedos, booze, cigars, and women. I think Bob Hoskins would work marvelously in this role.
The Riddler - I hope they don't drag this series down with doing more after the supposed planned trilogy with Joker/Dent. The character, and in this case the actor, deserve more than a cameo. My pick? Edward Norton. He is fast becoming, if not already, one of the best actors today. He, along with Liam Neeson, saved Kingdom of Heaven from being absolute shiite. Check out Primal Fear and Fight Club, he's cerebal too. And he'll look awesome in the suit and bowler cap.
Catwoman - I like the approach of Year One and The Long Halloween. The prostitute who becomes a thieve and moves up into high class society. This is early in the Batman mythos therefore she has to be young......say 20. Kiera Knightley is already an action star and can actually act.