Now this is unconfirmed news at this point but it's potentially big news so it had to go up.
A Batman fansite has recieved apparently legitimate information stating that Dark Knight director Christopher Nolan does not wish to film another Batman movie. Nolan took the death of Heath Ledger hard and originally the Joker was intended to return in a reprisal role with Ledger in the third film but now with that not a possibility Nolan can't face returning.
Speculation so far includes that if this is true then Nolan might still produce, other, most cynical speculation is saying that Nolan is playing the studio for more cash. Highley unlikely, Nolan could write his own cheque after Dark Knight and he doesn't need to hold out for cash.
As soon as this is confirmed or boshed i'll post.