Everybody's done the traditional Christmas songs, but I really like it when they jazz it up a bit. These are my favorites.
7) God Rest Ye Merry Gentlemen — Jars of Clay
6) It Came Upon a Midnight Clear — Caedmon's Call
5) Little Drummer Boy — Jars of Clay
4) O Come, O Come Emmanuel — Big Daddy Weave
I couldn't find a video — or even the whole song — but it's too good to not list. This link will take you to Amazon where you can hear a clip.
3) What Child is This? — Mercy Me
2) Silent Night — Jaci Velasquez with Burlap to Cashmere
This arrangement, which I've seen called One Silent Night, is a combination of Silent Night with her God So Loved to beautiful effect.
1) I Heard the Bells on Christmas Day — Casting Crowns
This arrangement of the old poem manages to be heart-rending and hopeful as well as beautiful. It is absolutely worth your time to listen. Twice.
Honorable mention: Anointed's version of Joy to the World is a lot of fun, but I couldn't find a good link. A sample can be heard on this album on Amazon.