I believe they need to get away from the normal path of the batman movies sort of like with TDK but bigger. Get away from going to catwoman, robin, normal bad guys etc...
My suggestion is to go with a team up with another DC hero, maybe a team up with Flash, The Green Lantern, Wonder Woman etc (JLA anyone?)... Then go with a bad guy(s) that has never been seen in batman movies before, my suggestions would be Clayface, Mad Hatter, Man-Bat or a JLA enemy etc... Use the same dark theme as TDK and ofcourse keep something from the base batman story arc but do something different, also would be a good chance to lead into JLA (look at Marvel, they are doing it right with The Avengers).
Ofcourse they could always go the NightWing/Batman Beyond route but thats for whole another time. That is my suggestion and i am sticking to it.