Music for Buffy Film Project-Help Please!

Hi all-

I am doing a project for school for a film editing class and would like to enlist the help of some fellow Buffy fans. The subject matter of the project has been left up to me, so of course, I am choosing to use my favorite show as the topic. Anyway, I would like to do some kind of collage of the 7 seasons accompanied by music. I am almost done with the clips themselves, but my dilemma is, what music to use? So here's the thing I need your help with-First,if you had to pick one song to be the theme for Buffy, for all seasons, what would it be? And secondly, if you had to pick a theme song for each season, what would it be? I would love to hear everyone's ideas. Thanks!