I copied this from Slickdeals:

Amazon starts the free Christmas music early--including veggietales Christmas I always have a Christmas section on my MP3 player for the holiday season and have been very happy that for the last few years tons of free songs have been around different places. Looks like Amazon is starting early.

Whole albums and sampler Albums:
VeggieTales - the Incredible Singing Christmas Tree [amazon.com]
-Hey, my kids will love it even if I don't...
Sugo Music - Free Holiday Sampler [The Very Merry Christmas Sugo Holiday Sampler]
-classy instrumentals
Chacra World Music Holiday Sampler [amazon.com]
-2 instrumental, and 3 vocal a better mix than the next sampler
Timeless Christmas (Amazon MP3 Exclusive Sampler)
-An ok odd mix: 2 old fashioned, 2 annoying voice, and 2 Michael McDonald songs

The Karaoke Channel - Best Traditional Christmas Songs
-each song has instrumental and vocal "tracks" -- nothing amazing

The Bell Medley [amazon.com]
Deck the Halls [amazon.com]
-60's surfer rock instrumental--good
Do You Hear What I Hear [amazon.com]
Winter Wonderland [amazon.com]
This Christmas [amazon.com]
Christmas Train [amazon.com]
-well, maybe the kids will like it...
Deck The Halls [amazon.com]
-nice instrumental
I'm Your Santa [amazon.com]
-upbeat bluesy
Rudolph the Red Nose Reindeer [amazon.com]
-timeless song of Rudolph the Red Nose Reindeer. Turn this one up. It's a little hard to hear.

I'll try to add more as they become available.