OK, don't laugh...Kathleen Battle's Christmas concert with the Harlem Boys' Choir is actually really beautiful.
I also saw a "Celtic Christmas" special on OPB(?) once that I've been trying to find ever since. I just remember randomly switching channels and coming upon a group singing the Christ Child's Lullabye, which is my very favorite Christmas song (I've been addicted to it since I heard Anuna sing "Suantrai" with Gaelic lyrics on their first album).
I also like Loreena McKennitt's "A Winter Garden."
Moll