Oh, I'm right there with you! I would probably sing carols all year long if people wouldn't look at me funny.
I especially love singing them acapella and ust listening to the voices harmonize - beautiful!
O Come, O Come Emmanuel
O Holy Night
Joy To the World
Angels We Have Heard on High
and this one is not really a carol, but I love "Mary Did You Know?" I got to sing this as a duet in a program one year with the most fabulous tenor I personally know, and it was magical. It is very hard to sing when you are crying, though!