I would like to see Catwoman. I disagree that she wouldn't fit into Nolan's world. She is one of the easiest to adapt. Ignore the whole 'brought back to life by cats' idea, because that was Burton and co's invention. Catwoman in the comics is basically just a very skilled catburgular who has a long-running lust/hate relationship with Batman. And her alter ego Selina Kyle = instant love interest for Bruce Wayne.
Obviously she couldn't be the main villain, for starters because she's not really a villain, more of a anti-heroine and she doesn't pose much of a threat. So I'd like to see Two Face back. The Riddler could be interesting. Although if he leaves riddles that needed to be solved otherwise things would get blown up, etc. it would be too much like the plot of TDK. Some reinvention would also need to be done because in the comics he's usually not taken very seriously as a villain. And if you had him and Two Face together, it's like Batman Forever all over again. Although much better, probably.
Who knows, The Scarecrow could pop up again. That would be quite funny. And then there's Ra's. We never actually saw him die remember. Although I doubt they'll go down that route. I also think they want to tackle at least 1 more villain that hasn't been seen in a film before so...hmmm.