It's that time of year again:

Rudolphus rubrinasus fulgentissimo naso,
vidisti et si eum dicas quoque candere.
Omnes tarandi ceteri ridebant vocantes nomina;
non sinebant Rudolphum interessa ludentes.
olim crassa nocte Christi, Nicolaus it dictum:
“Rudolphe, naso tam claro, agesne traham meam?”
Qui tum tarandis amor conclamantibus eum,
“Rudolphe, rubrinase descendes historia!”

... hear it performed the gang at St. Bart's ... And if you need Jingle Bells:

Consuli manu
Mappa decidit,
Acer cum curru
Equus exsilit.
Pone nos sonant
Carcerum valvae.
Quam circenses delectant!
Quam gaudent aurigae!

Tinniunt, tinniunt
Usque phalerae.
Quam libenter audiunt
in cursu aurigae!

Illic meta stat;
Flecte quadrigas!
Qui non evitat,
Frangit is rotas;
Concurrunt equi,
It caelo fragor;
Ruunt currus commixti,
Ubique fit cruor.

Tinniunt, tinniunt
Usque phalerae.
Quam libenter audiunt
in cursu aurigae!

(lyrics via ingeb.org)

... or Silent Night:

Sancta nox, placida nox!
Nusquam est ulla vox;
Par sanctissimum vigilat,
Crispo crine quieti se dat
Puer dulcissimus.

Sancta nox, placida nox!
Certior fit pastor mox
Angelorum alleluia;
Sonat voce clarissima
Iesus salvator adest.

Sancta nox, placida nox!
Nate Dei, suavis vox
Manat ex ore sanctissimo,
Cum is nobis auxilio,
Christe, natalibus.

(also via ingeb.org)

Some additional and/or alternate versions of Christmas songs in Latin at KET ... Harry Maynard's page is also full of useful stuff ... About.com Ancient History Guide N.S. Gill has some of the more 'traditional' offerings of the season ... I note that Bolchazzy-Carducci carries a cd of Latin Christmas Carols