Have you ever listened to 'Locking Up the Sun', by Poets of the Fall? That song is also a good Batman/Superman song--not so much a love song, maybe, but I think the lyrics are reminscent of both of them, I think, their contrasts and their similarities ...

Here's a link to the video, if you're curious:
http://www.youtube.com/watch?v=Iap7PpYNcXQ