If there were a particular inspiration for the next film, I'd like it to be Chinatown and other modern Noir films. Nolan has already proven that he rocks at this with Memento.
I don't know the particulars, but Catwoman could be the femme fatale - the woman/love interest who enlists Batman's help, but who turns out to have nefarious selfish aims.
The Riddler would be connected somehow to Catwoman and causing havoc all over Gotham as a Zodiac type seriel killer. In the end, we'd find that the Riddler was actually a distraction hired by the Penguin in order for him to trigger a gang war in Gotham without Batman's interferrence-thereby profiting with his gun smuggling operation. The climax would be an all out street war in which the gang members are supplied with high end technology from the Penguin.
I'd like to see snow in Gotham as well, and maybe Batman with some some scruff going. I feel like the next movie should be a mystery; it would depict Bruce as someone who's finally losing himself in his costume... so much so, that he becomes obsessed with uncovering the Riddler's bizarre puzzles. He becomes so diverted by trying to find the Riddler and Catwoman, that he misses the real threat... the Penguin.
I'd also like to see Batman bleed a little.