Thanks for starting this thread Andy.
I love Christmas music. There are way too many for me to post a very comprehensive list but here are a few that really stand out.
Sleigh Ride - there are many versions of this song that are great, but my favorite is by Phillips, Craig & Dean. I actually sang back-up for them once which was an awesome experience.
Little Drummer Boy - again, there are many versions of this that are great, but Audio Adrenaline and Jars Of Clay do my favorite versions.
O Holy Night - Mario Lanza does a version of this that is absolutely amazing. I love hearing just about anybody do this song though.
God Rest Ye Merry Gentlemen - Phil Keaggy did a great version on an album called Our Christmas years ago that I can't seem to find anywhere.
The Christmas Song (Chestnuts roasting on an open fire) - It's hard to beat Frank Sinatra for this one, but Garth Brooks does a great version of this song believe it or not. Bryan Duncan does this song very well too.
Let It Snow - Russ Taff does my favorite version of this one.
Mary, Did You Know? - Michael English nails this one, but there are a lot of great versions by other artists
Do You Hear What I Hear? - Third Day does my favorite version, but again, many people do this one very well also.
This Christmas - an original Christmas song by Toby Mac
This Baby - another original Christmas song by Steven Curtis Chapman
The Form Of Man - an amazing original Christmas song by Bryan Duncan
Please Come Home For Christmas - Bryan Duncan does my favorite version, but the Eagles (who wrote it, I think) of course do it well also.
I'm leaving out a whole lot of favorites, but I could do this for days and probably not list all of them.