if they make another one i really do hope they pick a good villain.
joker and twoface didn't have powers or anything, just complexes
scarecrow had hallucinogens, which are very much a real thing
raz al ghul was a ninja or something (didn't realize it was him until the end of the movie)
riddler would be a dumb choice: joker was pulling strings the whole movie, i really don't see how setting traps calmly and collected would be much different than setting traps and laughing crazily
everybody else is pretty ridiculous: croc, clayface, ivy, & manbat would be my picks, but they really wouldn't fit with nolan's universe of reality. the penguin pretty much just sucks.
i'd like to see mr. freeze, but again he is very otherworldly. i mean even without the ice ray gun, he's a dude that is frozen alive or what?
honestly it would make a lot of sense to use catwoman, considering that in the dark knight rachel dawes died, leaving no love interest. i don't really like catwoman but she is a pretty important part of batman, and probably the most well known villain outside of joker.