I think Hagrid is quite likely, myself. He would certainly have a massive emotional impact, but he's not really that important in the grand scheme of things (though having said that, if he survives, I bet he'll have a big hand in the final battle just because shitty characters with not much going for them always do in stories like this *coughhobbitscoughcough*).

I'm also liking the theory that Dumbledore will snuff it at the end of this book, leaving a cliffhanger for book 7, though if he doesn't, either he or Harry will be gone by the end of the series--I just can't see the side of good triumphing without at least one of its two main forces sacrificing themselves. Maybe he'll die to save Harry, that would be suitably sentimental.