Samuel Barber's Agnus Dei Yes, I know it was originally his Adagio for Strings which he added lyrics to later is one of my favorite works. I really liked that accordion version.
I first ran into this choral version on the Homeworld soundtrack. Perhaps I like that recording more. www.youtube.com/watch?v=fXRJBK8oJSA
I'm a classical violist, and this is a ton of fun to play. Most people don't realize how much fun it is to perform classical music at a high level. Incredibly satisfying.