Emerson, Lake and Palmer's "Father Christmas" has always been a source of amazement to me: it's endlessly popular on the radio stations around here every year, and nobody seems to notice how depressing the lyrics are. Just part of the holiday noise (and I for one love Christmas, thank you very much).
The song isn't exactly "folky," but you could make it work with a guitar and voice, or some such simple ensemble.
-Glenn