Colin Farrell was cast as the Penguin. He was also in Daredevil.
Andy Serkis will play Alfred. He's in the MCU.
Zoe Kravitz will play Catwoman, who she also voiced in Lego Batman, so there's another hint for her.If graphic novels are included, then Paul Dano can join because he was in Cowboys and Aliens and he was cast as the Riddler.Another name I found was Peter Sarsgaard, pretty obscure but he was in Green Lantern as Hector Hammond, so feel free to decide whether he's in or not.
Also, I recently learned that Christian Bale is in talks to join Thor 4, so I'll be on the lookout for that one.