I'm surprised no one has made mention of Joseph Gordon-Levitt having been in talks to play some unnamed role in this film. I've been searching for awhile, but... can't seem to find any updates as to whether this was finalized or not.
As for the villains, I really am both pleased and somewhat disappointed. Having the feline-like femme fatale Selina Kyle in the movie was a very smart choice I think. After the death of Rachel, Bruce transitioned more into the role of Batman, I think. With her being in the film, I see Bruce finally, truly becoming Batman. In the first film, it was all new. Crazy young man becomes hero. The second, he deals with the repercussions of his choices in the first film and is faced with that issue of "Who am I?" as well as questioning whether or not he is capable of taking on the responsibilities be rashly forced upon himself. I've a feeling Kyle will be good for him, considering the history between the two characters in the series, and will be very influential in him taking what I feel are his final steps to truly embrace his mask.
Bane... Bane I feel is a very interesting choice simply because he, like Catwoman, is one of those characters that has shifted back and forth from villain to hero and back again so may times that the character resides in that gray area of morality that seems to be the theme of the Batman franchise right now. Considering it is Tom Hardy, I've a feeling that finally we will be seeing Bane's more innocent and intellectual sides. (Okay, I know he's not innocent, buuut... he isn't this mindless evil brute people seem to assosciate him with entirely. =/)
The flaw though that I see is that there is no TRULY villainous characters here. I don't know... Nolan has a knack for pulling this stuff off well, but.. I'd say a more villainous character is needed. Probably someone who sets Bane off on his rampancy or something. As someone already stated, I think that Hugo Strange would be absolutely perfect here. His knowledge as a Doctor, and his history of making genetically modified monsters out of people seems like something that would go well here. Plus, given Batman's current situation, it's not entirely unbelievable given his character to be attempting to aid Commissioner Gordon and the GPD in the capture of Batman while simultaneously influencing the criminal underworld. It could also put an interesting twist on the sense of right and wrong as well in that Bruce Wayne could see him as a good person and the others as villains, and have that point of view be shifted. It's not unlike Nolan to mess with a person's perceptions like that, so.... it's not completely impossible. Especially given the revelation of Levitt possibly being in the film and Gary Oldman's hinting of a possible 3rd villain that's been around for a loooong time in the Batman universe, it's not implausible.
Robin is not needed, in my personal opinion. This tale is about Bruce's rise to being a hero. Robin came in muuuuch later. it doesn't sit well with me at all.
Regardless, Nolan has given us two amazing Batman films so far and I don't doubt that the final in his trilogy will be the crowning jewel.