It's not a Christmas tune, but if he does "Ave Maria" he's got to do "Danny Boy" too. You can't have a Catholic funeral without either one. At least not any I've been to.
Actually, in all seriousness, I think that an album of traditional Irish/Celtic songs, perhaps with the Chieftains (ala Van Morrison with the album, Irish Heartbeat, which is one of my favorite albums of all time), would be just excellent. His voice is very well-suited to such music. Oooh, I'm getting goosebumps just thinking of hearing him do "Carrickfergus"! <---Happy Green Irish Smiley