While it is not specifically Christmas one of my favorite albums for this time of year is "December" by George Winston (very beautiful piano music). The single greatest piece of music for this time of year has to be the "Hallelujah (Chorus)" from "Messiah" by Handel. The entire work is great but that single piece of music sends shivers down my spine every time I hear it.
Ok this will probably get some comments but "Christmas Portrait" by the Carpenters is excellent Christmas music. Karen Carpenter had a beautiful voice that made some of these standards some of the best I've ever heard. If you have never heard it find a copy because it is a great listen in front of the Christmas tree or fireplace.