Happy, merry, joyous, cheerful, or otherwise good:
Christmas, Yule, Hanukkah, New Year's, Kwanzaa, Solstice, Saturnalia, Ashura, St. Nicholas Day, Human Rights Day, Asarah B'Tevet, Yalda, Boxing Day, Bacon Day, Pearl Harbor day, Agnostica, or anything else you celebrate this time of year.
(thanks,
http://www.brownielocks.com/DECEMBER-2011.html)
I don't even know what some of these things *are*...