There's one by the Ramones if i'm thinking correctly. Don't quote me on this though.

I refer you to THIS:
http://www.musicbanter.com/general-m...as-covers.html

Vanessa Carlton-Greensleeves

Basshunter, a swedish DJ, did a Jingle Bells cover. Not sure where to find the song but it is on youtube here:

hxxp://youtube.com/watch?v=UGquX-SQtZA

the knife - christmas reindeer
bleu - snow day
nuclear saturday - winter wasteland
simple plan - my christmas list
bright eyes - blue christmas
sufjan stevens - that was the worst christmas ever
playradioplay! - little drummer boy
danger:radio - all i want for christmas is you

"How To Make Gravy" by Paul Kelly is a Christmas song with a difference. It is about a person in jail who will be "inside" while their family is celebrating Christmas.

The Barenaked Ladies - I saw three ships
I think its off an entire album of christmas songs.... Yep, "Barenaked for the Holidays"

Giant Drag did a pretty decent cover of Silver Bells.