My favourite (sorta) non-religious Christmas song is by Steve Earle--it's the last track on his "Copperhead Road" album, and it is an ingenious rewrite of the Christmas story--"Nothing but a child"

My other (less tasteful) favourite is "walking round in women's underwear" --a parody of "walking in a winter wonderland" I think it is listed in the mudcat song library.

I'm a practicing Christian by the way, and I love the whole Christmas thing.