Almost all of these are probably considered "uninspired", "safe" or "cliche" but I don't care, those are just buzz words that mean "good/great choice" to me, lol... I'll throw a few alternate choices in parenthesis..
Batman - Ben Affleck
Nightwing - Ian Somerhalder (Dylan O'Brien, Logan Lerman for younger)
Catwoman - Kate Beckinsale (Lauren Cohan, see below)
Commissioner Gordon - Bruce Willis (Bryan Cranston)
Sarah Essen Gordon - Elizabeth Mitchell (Elisabeth Rohm)
Barbara Gordon - Emma Stone (Emmy Rossum, Mary Elizabeth Winstead)
Harvey Bullock - Michael Madsen (Wade Williams)
Renee Montaya - Alice Braga (Lauren Stamile)
Maggie Sawyer - Connie Nielsen
Joker - Jared Leto
Penguin - Ray Winstone (Mark A. Sheppard, Timothy Spall)
Scarecrow - Jackie Earle Haley (Adrien Brody, Sharlto Copley)
The Riddler - Robert Knepper (Garret Dillahunt, Michael Sheen)
Two-Face - Jon Hamm (Michael C. Hall)
Mr. Freeze - Ralph Fiennes (Mads Mikkelsen, Jason Isaacs)
Deadshot - Will Smith
Deathstroke - Gerard Butler (Sean Bean, Jeffrey Dean Morgan, Jim Caviezel, Johnny Messner)
Black Mask - Kiefer Sutherland (Jeffrey Donovan, Cole Hauser)
Harley Quinn - Margot Robbie
Poison Ivy - Eva Green (Olivia Wilde, Melanie Laurent)
Ras Al Ghul - Christopher Heyerdahl (Alexander Siddig, Demian Bichir, Jordi Molla)
Talia Al Ghul - Olga Kurylenko (Berenice Marlohe, Nazanin Boniadi)
Hugo Strange - Michael Nyqvist
And with the typiest typecastings of all time....
Carmine Falcone - Al Pacino
Sal Maroni - Robert DeNiro
Hate on it if you want, but who wouldn't want to see Pacino/DeNiro playing mobsters in a Batman movie? If you say you wouldn't, you are dead to me, lol. I could come up with other choices but I probably wouldn't even have the Mod Bosses in these new Batman movies so I'll stick with the Legends. While Charlize Theron, Emily Blunt and Eva Green could all easily play Catwoman, I have them all playing different roles in the DCU. Eva Green as Ivy as you can see, Blunt as Hawkgirl and I have Theron as Circe. Eva is literally perfect casting as Poison Ivy IMO. Beckinsale has been my top choice for Catwoman forever and she's still age appropriate for Affleck. Ra's Al Ghul is always my most difficult, I change my mind on that all the time. I've been trying to go with Foreign choices for the Al Ghul's. Kiefer as Black Mask is simply because I want to hear his voice coming from behind that mask, I think it would be an awesome fit for that reason alone, haha. I know most people say Somerhalder is too old for Grayson but I don't agree, he looks younger than he is and he's just a great fit for the character to me. Joseph Gordon-Levitt is the only choice I prefer over Somerhalder but I don't see that happening for multiple reasons. As I've said before, my top 3 choices for Penguin all died, James Gandolfini, Philip Seymour Hoffman and Bob Hoskins. Winstone is the best fit left by far IMO. Deathstroke is another difficult one, I go back and forth on a bunch of candidates all the time.