Yes to the asexuality suggestion. I've got a story in progress right now that has a male and female protagonist that are both pretty much asexual (in a culture that's very accepting of it, so it's not a Big Deal), and I'm hoping it messes with the heads of some people who read it and think "but the hero and heroine *have* to fall in love!"
I would like to read a book like that. At the same time, though, unless it was clear from the beginning that the characters didn't thin kthat way, I'd be afraid they would fall in love at the end of the story. I've read far too many books where the author had both characters start out only thinking of their relationship as friendship, but then "fall in love unexpectedly" at the end.