Coope, Boyes and Simpson have done a couple of excellent christmas cd's. Also the 'mystery plays' cd by Home Service is half christmas-related. I don't know if either of these will be easily available if you are not in the UK though.

Johnny Copin has done a couple of cd's of traditional songs from the west country area of England. If you want something more folk-rock then Jethro Tull's christmas album has some good tracks.

For interesting individual christmas songs then my favourites would be 'Winter Song' by Lindisfarne, 'Christmas Eve Can Kill You' by Everly Brothers (amongst others) and Stan Rogers' 'First Christmas Away From Home'.