Personally, I don't really like Neville/Luna. No offense :) It just seems like they are often thrown together because they are outsiders, but other than that, I really don't think that they have that much in common.
I mean, if you look at the scenes where Neville and Luna are together in the 5th and 6th books, Neville almost seems to be intimidated by Luna because of her "weirdness". Neville proves himself to be brave, but in the 5th and 6th books he is slightly more insecure when surrounded by his peers. And while he feels comfortable with Harry, he seems to weirded out by Luna.
IF Nevilla and Luna were to be together, it should happen over the course of the 7th book after fighting together and rebelling against Snape and the Carrows. I think that id there were to be a romance during that time, it should start because they were spending so much time together, and because they eventually grew to admire each other's braveness, and they possibly got to know each other better.
But I don't know, something about this pairing in a serious relationship is just so off for me. I guess I'm just weird like that :p