I discovered a fairly new Christmas song several years ago on the 1996 CD “Carol,” by the American Boychoir.  The song is called This Christmastide. It’s also known as Jessye’s Carol, because it was originally written for soprano Jessye Norman, I believe.  Sometimes the Boychoir’s arrangement gets fairly complex, but I feel the song is at its best when they sing in quiet unison or simple harmony.