What about Sarah Brightman's version of "Ave Maria"? It is hauntingly beautiful.

I wanted to sing it at my own wedding (I sing Sarah's material) but due to nerves didn't want to sing live and then ran out of time to cut a CD.

Dona Vina (spelling)? sings a lovely ballad called "in love with you". Also beautiful.

Another idea is Shania Twain's "You're still the one" and there is another typically wedding type song on the same CD but the name totally eludes me right now.

Ummm, thinking ............. Celine Dion's "Falling into You" (understand she is not everyone's cup of tea).

Those were just a few off the top of my head ideas.

Good luck - would love to know the final choice.