From SuperheroFlix :

Warner Bros. Pictures has set the release date for The Dark Knight, the sequel to 2005's Batman Begins for July 18, 2008. The Film will star Christian Bale, Heath Ledger, Michael Caine and Gary Oldman.

In the film, Batman and Commissioner Gordon find alliance with a newly appointed DA Harvey Dent to stop a vicious killer with a warped sense of humor known only as The Joker, a threat to both the good, and the evil of Gotham City.

July 18 means one week before The Hulk opens. I think it's good considering that no other big movies released around that date.