I'd like to see Harry end up with Luna, so that's who I voted for. But I'm not absolutely sure that's what will happen. Mumbleberry's post on page 7 gives a lot of good reasons why they'd be compatible, and I'd like to point out a couple of other things that seem pertinent to me:
1) I think Harry needs some things that Luna has. Serenity, for example. I think that if Harry can learn to be at peace with himself, he will become a much more powerful wizard. (Side note: I believe that the character development of Ginny and Neville in recent books reflects this - both characters seem more comfortable with themselves now, and they also both appear much more powerful than we would have thought of either of them prior to book 5.) So I think that JKR definitely has plans for interaction between Luna and Harry, in order that he can learn from her.
2) I've noticed a couple of people using the fact that Harry met Ginny on the platform at Kings Cross as evidence that Harry & Ginny will be together in the end, because that's how JKR's parents met. According to interviews in
Scotland on Sunday and
The Times, they actually met on a train that left King's Cross, not at the station itself. So that might actually disqualify Ginny. But Harry did meet Luna on the train.
3) Harry and Luna wind up under the mistletoe together. Nothing happens, but it could be foreshadowing. (I think someone may have mentioned this earlier in the thread, and I'm sorry for not giving them credit, but I couldn't find it again when I went back to look.)
4) If I remember correctly, Hermoine and Luna quarrel a couple of times about their respective beliefs. But the quarreling stops around the time that Harry does the interview with Rita. I
think the other thing that changes around that time is that Luna interacts with Ron less and with Harry more. I think it's possible that one thing that happened offstage was a clearing of the air between Hermione and Luna (maybe conerning Ron), and I think that would bode well for a relationship between Luna and Harry.
Having said all this, I'm still not convinced they're going to end up together... partially because Luna is the only character I can think of besides Dumbledore who is so serene about the prospect of death. It wouldn't surprise me if Luna sacrificed herself at a critical point in either Book 6 or Book 7, simply because she was the first person to see it as a possible solution to whatever problem was being faced, and act accordingly.