OK, this isn't really a "Christmas" hymn, but I first heard it on a collection of Christmas songs by the Dale Warland Singers. It is beautiful, called "Jesus Christ the Apple Tree", here done by the choir of Kings College, Cambridge:
I refuse to give in to popular ignorance and put up a bunch of the music from Handel's oratorio The Messiah. It is an Easter oratorio. Yet, there is one passage, "For Unto Us A Child Is Born", that can, with justice, be sung at Christmas. This is Robert Shaw Conducting the Atlanta Symphony and Chamber Chorus:
One of my favorite Christmas Songs is "Coventry Carol". I guess I just have a soft spot for English hymnody. This is the Royal College of Music Chamber Singers:
To you and yours, one last time - Merry Christmas, and may you be richly blessed by the birth of hope and life and light.