Out of Thin Air from Aladdin and the Kind of Thieves is a pretty duet! That's in the Disney Princess book.
Once Upon a Dream is a classic!
Love Will Find a Way from Lion King 2 is pretty!
You could sing Let's Get Together as a male/female duet, i think that would work fine.
i think that's all i can think of right now. if i know any more i'll let ya know.
"Have a child for warmth and a baker for bread and a prince for... whatever!"