If you haven't seen the movie (see: living in a cave) then don't read any further, as there will undoubtedly be spoilers to follow. At the end of Dark Knight, Harvey Dent's fate was left a tad bit ambiguous. While superficially it seemed sure that Two-Face was dead, upon repeat viewings there became a slight possibility that Harvey Two-Face was indeed still alive at The Dark Knight and could have made a return in Batman 3.
Eckhart asked Nolan about whether or not there was a possibility he would return for a sequel, to which the director delivered a flat "No way". Nolan confirmed that Harvey is in fact dead, and subsequently silenced half of the "bat chatter" on the internet.
Warner Bros. have stated that they would like to have the third Batman movie released in 2011. No official plans have yet been announced.