batman 3 starts shooting in april 2011

Batman 3 will start shooting April next year and Director Chris Nolan has stated that Heath Ledger will not be replaced as The Joker in any of the sequels. According to Dimewars.com,

For me, Heath was the definitive Joker," Nolan said, "It wouldn't feel appropriate to readdress that character." 

On Entertainment Weekly:

Although Nolan, his brother Jonathan, and David S. Goyer are still working on the script, an insider confirms that, although subject to change, Warner Bros. is indeed on track for an April start date, and Christian Bale, Morgan Freeman, Michael Caine, and Gary Oldman are attached. 

But Warner Bros. has also penciled in the next Batman for a July 20, 2012 release date. The studio was determined to set a definitive release date this far in advance due to the strong slate of other superhero movies to be released in the next two years.