My thoughts (thanks to too much free time on my hands)...
There's been some talk that Nolan won't come back for a third. If that happens Bale probably doesn't come back. I imagine this is just business to make sure WB backs the Brinks truck up to everyone's house. To me there has to be a third film because of the story being told...
BB- Rise of Batman
TDK- The fall of the dark knight
B3- Redemption of Batman
You could leave it where it lies and it would be ok, but the end makes you feel like there is more story to tell. Yeah it will be hard to top this movie. They essentially made ESB or Godfather 2 with this franchise. I feel like these filmmakers are capable of making a ROTJ instead of a Godfather III. To do so you're going to need some recognizable villain(s) who are capable of putting Gotham (and Batman) in severe peril so the Batman can be redeemed. Here is a couple of ideas...
The Riddler: First off, forget the over the top Frank Gorshin 60s Batman or the horrible Gorshin inspired Carey Riddler from Batman Forever. This Riddler needs to be the real deal. Lose the jump suit and the corny laugh and make him the intellectual equal of Batman. Make him a brilliant engineer and detective who comes up with elaborate schemes and build elaborate death traps in search of the answer to the greatest riddle in Gotham: Who is Batman? His hyper-OCD nature is what fuels his criminal passion. Possibly base some of his crimes on the Zodiac killer. It is going to be hard to make him not just a Joker replica, but reinventing the Riddler character is something Nolan would do and could make him just a strong of a supervillian.
Casting: Don't get a comedian. If they could actually get Daniel Day Lewis to play him it could be great. Get someone who can do dark and brainy but intimidating.
Catwoman: This was my initial choice but after thinking about it I'm not sure she's the best choice as a main villain. I'd love to see her as part of this franchise because they could make her into something special. The cool thing about Selina Kyle/Catwoman is she shares in the duality that Bruce Wayne/Batman lives in. Make her like a Thomas Crown character: a bored socialite who begins to steal from her rich friends and lives by her own moral code. Because of this she would see right through the facade of Bruce Wayne. Making her a shade of gray, one minute a foe the next minute a friend, fits perfectly in this world Nolan has created. It also gives Bruce Wayne a new female to interact with and one he doesn't have to continually save.
Casting: I read where Kate Beckinsale was interested. I think she could play both roles effectively much like Bale does.
Black Mask: I got looking into lesser known Batman villains and this one stuck out. Leaving behind the bizarre aspects of his origin, make him a failed business man who resorts to a life of crime and ascends to the head of Gotham's underworld. With the top bosses eliminated by the Joker and the Joker himself incarcerated there would be a power vacuum in the mob. With a "freak" in charge the mob becomes even more violent looking to reclaim what was theirs before Batman came along. Another important aspect of this is Black Mask's hatred for Bruce Wayne, which will indirectly put him against Batman. Penguin could easily fit this role too but I think trying to portray him in a realistic way is too difficult.
Putting too many villains in a movie can be dangerous (see Spiderman 3, X-Men 3) but if they are all unified in one common goal (finding out who batman is and destroying him) and the story being told has a logical progression then it could work. And remember while he's fighting to save Gotham he's going to have Commissioner Gordon trying to catch him as well.
Just my take.
Edited by Rock, 23 November 2011 - 09:38 PM.