One of the best parts of Batman is that sheer volume of non-fantastic super villains he has in his rogues' gallery. Seriously:
Crime Families
-Falcone
-Maroni
-Vitti (they could add to Gordon's connection to Chicago, as they are based there.)
Mobsters/Industrialists
-Rupert Thorne
-Sal Valestra
-Roland Dagget
-Powers Family
-Buzz Bronski
-Cobblepots
-Roman Sionis (Pre Black Mask).
The Muscle
-Victor Zsasz
-Deadshot
They could explore the corrupt police officers:
-Loeb
-Flass
-Branden
In the background, they could have characters such as Hugo Strange advertising his practice (or perhaps even having a talk show,) Mayor Hill, Leslie Thompkins, and so on.