Potentials for the next movie: Some Options
Penguin: just a mob boss with a quirky sense of dress and a pointy nose and funny name (Oswold Cobblepot? Really?What kind of parents do that to their kid and don’t expect him to grow up damaged?).
Although he’s one of the most recognizable/famous Batman villains, using him in the 3rd movie wouldn’t really add anything to the story that we haven’t seen before (via Carmine Falcone and the misc. mob bosses in TDK).
Catwoman: She’d give Batman a chance to expand his crime-fighting duties beyond just street crimes and into more investigative things, like burglary. Could help him get back into the Gotham PD’s good graces by working with them to recover things she’s stolen, but it might be too quick a reconciliation after the end of TDK.
While she is a great Batman villain (definitely one of the most recognizable names), I don’t think she should be in the next movie mainly because she’s an actual romantic interest. Of all his relationships, I’ve always felt like the ones that were closest to working out were Selina Kyle and Talia al Ghul. Since Talia doesn’t seem to exist in the Nolanverse (or wouldn’t be able to without a little evasive manoeuvring around the backstory Ra’s gave us in BB), Selina becomes the one love interest that should be fully delved into.
The sexual tension between Batman and Catwoman is what makes her an interesting villain, and without that done properly, I don’t think she’s worth it as a villain for the 3rd movie. Because Rachel only just died in TDK, it’d be too soon for him to jump straight into a real relationship.
Firefly: minor arsonist with a quirk. He could easily be a throwaway started villain or super-tiny side plot, just for filler. His psychological issues make him interesting enough to be included.
Arson’s a crime we haven’t really seen before, and could be an opportunity for Batman to develop/display investigative skills as well.
Mad Hatter: uses mind control chips in people’s hats. It could be interesting to bring in a paedophilic Alice-obsessed aspect to him in order to make him darker and creepier. Plus, he could bring in a technological/sci-fi aspect with the mind control chips.
But, it’s messing with minds again, and I think we got enough of that with Scarecrow in BB. The danger is that his Lewis Carroll obsession might come off as ‘crazy just for the heck of it’ if not done properly; it might be difficult to justify a Joker-level of crazy and pull it off again with a seemingly random literary theme.