It's way early for me to be thinking about music (we're planning for next October), but I'm doing it anyway!
So here's the deal. I'm an Episcopalian Christian with a fondness for liturgy and Jewish roots. He's a lapsed Pagan from a Jewish family. I love music (I sing in choir), and I would enjoy singing a hymn/song or two as part of the ceremony. However, I'd have to find a song that everyone could feel comfortable singing -- which means nothing explicitly Christian (no Jesus), explicitly Jewish (no Hebrew), or explicitly Pagan (no Goddess). Something like "Simple Gifts" (the classic Shaker song) would work, since it has a beautiful message but doesn't invoke any specific deities.
So what songs are you all using, if any? How do you find something that everyone can feel good about? (I would raid the UU hymnal, except -- no offense, UUs, I have every respect for your religion as a whole! -- the music tends to be, well, boring to me.)