Arkvoodle said:
BANE.
We need to see someone who can challenge Batman PHYSICALLY; the last two have taxed him mentally.
Okay, let's get a refresher of villans who have already appeared in (recent) Batman Movies and which movies they appeared in (as well as the actors who played them). (Wiki Source [http://en.wikipedia.org/wiki/Batman_franchise_media#Theatrical_movies])
Batman: 1989
+The Joker (Jack Nicholson)
Batman Returns: 1992
+Catwoman (Michelle Pfeiffer, not Haley Berry)
+The Penguin (Danny DeVito)
Batman Forever: 1995
+The Riddler (Jim Carrey)
+Two-Face (Tommy Lee Jones)
Batman and Robin: 1997
+Mr. Freeze (Arnold Schwarzenegger)
+Poison Ivy (Uma Thurman)
+Bane (Robert Swenson)
Batman Begins: 2005
+Carmine Falcone (Tom Wilkinson; Yes, the Falcone crime family is actually canon, though not quite as famous as the more-costumed villans)
+Ra's al Ghul (Liam Neeson)
+The Scarecrow (Cillian Murphy)
The Dark Knight: 2008
+The Joker (Heath Ledger)
+Harvey Dent/Two-Face (Aaron Eckhart)
In other words: all of the villans before Begins are going to be carrying real serious baggage that they're going to need a clean break from. I feel that only the Pengiun and Riddler are salvagable from those unfortunate movies, mainly because they were portrayed so poorly/cartoonishly that a more serious rehash of the character is possible.
And for those who believe that Batman needs a more physical opponent: I think that the new idea of Batman as more of a ninja/detective (rather than the head-on fighter that came to be in the 90's interations) would make such a move counter to the new feel of the movie series. Killer Croc could be done, but it just wouldn't make sense that a deformed hulk would suddenly appear in Gothum City. He probably could be done as an imported mob hitman targeting rival mobsters or Public/Corporate figures, but he couldn't be brought in targeting Batman himself because (a) the incident with the Joker would probably discourage any mob don from pushing forward with trying that again and (b) it just would feel like the same plot of The Dark Knight.
EDIT: As for Bane, the complexity of his background (Political prisoner and prison fighter with a high intellect and excellent education who gets used as a test subject for the Venom drug) and motivations (intially to simply be the one who takes down Batman) would be very hard to put into a movie well. Combine that with the Batman and Robin trainwreck that turned him into a mindless hulk and there is little reason to try this character any time soon.