First off. 8 Bit Collective has a thread going with some great Christmas songs. Check that out through this link.
Next up, the Gamewave Podcast has put together their latest show, which is completely dedicated to the holidays as well. So head over to gamewavepodcast.com and grab their latest episode!
Speaking of excellent podcasts with holiday themes. Also be sure to check out Hipster Please's latest episode of Radio Free Hipster for some holiday nerdcore and more (that rhymes!).
DJ RoboRob has released a Christmas EP which is worth downloading, you can grab that over at his myspace page.
The Oneups made an excellent rendition of Mario and Christmas themes entitled Super Mario Sleigh Ride. You can download it for free off of The OneUps website.
Check out Animal Style's page for plenty of excellent Christmas chiptunes.
Speaking of Christmas chiptunes, Eric Chiptunes also has some holiday cheer on his Myspace page, so check that out as well.
Hope this helps you get in the holiday spirit! and maybe sneak a few of these songs in at any christmas parties you happen to be at!