Kath, "How Can I Keep from Singing" is a great choice. I'd also suggest Si Kahn's "What Will I Leave Behind?" or Utah Phillip's "Hymn" Or "What a Wonderful World" by George Weiss & Bob Thiele, popularized by Louis Armstrong. I bet we come up with a bunch more, too.

(Maybe they're not in-yer-face athiestic, just universal & don't bother with mentioning deities, thankyouverymuch...

Cheers, Tom