Generally I hate christmas songs (although I do tolerate some of the better ones by bands like Wizzard & Slade),but there are two christmas songs I can happily play all year round:

1)Pogues/Kirsty Macoll-Fairytale of New York
(any song that sings about scum bags,maggots & cheap lousy faggots,has gotta be great)
2)Billy Idol-Yelling at the christmas tree
(a new addition this year,but the song just makes me think of me)