He's dead. Yeah, it was hard to determine and we've had some very cryptic hints from the actors but I believe he's dead. It won't matter though, the main things are the repercussions of his actions and how they will play into TDKR.
Here's why I think he's dead:
-He can't survive that fall (Batman can though). And if he could, he would also break his neck.
-We saw a memorial with Gordon giving a speech at the end
-DO NOT READ! SPOILERS!
I believed in Harvey Dent.