Or, maybe not of all time, but my five favorite Xmuss songs are embedded below:
The Pogues and Kirsty MacColl, "Fairytale of New York":
The Kinks, "Father Christmas":
Tom Waits, "Christmas Card From A Hooker in Minneapolis":
Robert Earl Keen, "Merry Christmas From the Family":
Tiny Tim, "Santa Claus Has Got the AIDS This Year":
If these songs don't put you in the mood, then I pity you. Merry You-know-what.