There are so many good and thoughtful posts on this topic. Please forgive me for being still too new to have figured out how to quote anyone.(which probably just requires reading the directions.)
While she is a very interesting girl, Harry will absolutely NOT end up with Luna. She's just too, well...herself. They might date, or have a strange and ethereal fling, but she's not his "true love" or whatever you want to call it. She's a teenage Sybil Trelawney.
I wanted to comment on the "Ginny is over Harry" ideas. Just because Ginny appears to be "over" Harry, i.e. she's going out with other guys, doesn't mean at all, that she's not carrying some deep feelings for him. We ladies, quite often in fact, will have a very special love that we conceal until we know the time is right. And can't you just imagine JKR writing this? Ginny finally having the oppportunity to confess that she's loved Harry since she was ten years old? And Harry realizing that Ron's kid sister has grown into a really beautiful young woman?
Someone else said that Harry and Ginny didn't "share" anything, but in the CoS, they share a very very powerful life and death experience that I think, will produce strong emotions in both of them a little later on. Ginny is like the Bruce Springsteen song. Her heart is a secret garden. She has not yet blossomed into the woman she will become. But just wait...just wait.
And she reminds many of us of a young Lily...