- Harry lives happily ever after. He goes on to become Hogwart's Headmaster, Minister of Magic or Quidditch world champion. Most likely, he marries Ginny Weasley, they have children who go off to Hogwarts and the cycle starts again.
- Harry dies in the process of killing Voldemort or at the hands of someone else. I think this is unlikely to happen, especially due to JKR's large number of hints that this might happen; if she really wants closure, the worst way to go about it in this postmodern age is to kill the character off. (see also: Superman, Buffy Summers, Sherlock Holmes)
- Harry lives, but somehow loses all of his powers, either because they're linked to Voldemort's, because he somehow "burns them out" or because he gets put into a situation where exposure to magic is deadly to him in the future. This is a fine classical ending, parallel to Prospero breaking his staff at the end of the Tempest.
- Snape turns out to be good after all (come on, you have to have seen this one coming)
- Draco does something to redeem himself and/or gets saved by Harry
- It turns out that Dumbledore had been using Nicholas Flamel's Sorcerer's Stone to extend his own life until the end of Book 1, when his supply started to run short and he had just enough to "put his affairs in order"
- Who lives? The main three characters, McGonagle, the Weasleys, Luna, Neville.
- Who dies? Voldemort, one more baddie (Peter Pettigrew, maybe?), plus one of the remaining good guys (could be Harry, probably one of the Phoenix people, maybe Snape)