In no particular ranking...
Sleigh Ride - Leroy Anderson
The Messiah - Handel
Nutcracker Suite (hard to beat a masterpiece)
Troika - Prokofiev (this is great, paired with the Leroy Anderson one!)
Carols:
O Holy Night (lyrics written, ironically enough, by an atheist)
Good King Wenceslaus
Chestnuts Roasting (esp the Nat King Cole)
Joy to the World (listed because of the audacity of the opening being simply a major scale played backwards!)
Angels We Have etc.
God rest ye merry (got to get a trad. English in there)
In the Bleak Midwinter (underrated, except by choral folk - really one of the greatest)(music by Holst)
O Come, All Ye (any choir worth the name will blow your socks off with this one)
Carol of the Bells (when the harmonies are well done, this is beautiful)
Hark the Herald (Mendelssohn writes damned good music)
Christmas song I never want to hear again because it's a tiresome festering ear parasite that will eat your brain:
Feliz Navidad
(The other one in this last category I don't even mention by name. You know what it is, you know it causes permanent neurological damage, nothing can be done to stop it!)