I haven't seen it this year, but I enjoyed Avery's christmas ale quite a lot last year. Celebration is good, too.
I also enjoy the Sierra Nevada Merry Christmas Ale (or whatever they call it) that comes in magnums. I have a small collection of magnums that I will be using for some of my own Christmas Ale.
On a lark, I picked up a couple bottles of Trader Joe's X-Mas Ale (or whatever they call it). It's contract brewed by Unibroue (one of my favorite breweries) so I figured it should be decent, particularly at only $5 a bottle. It's OK, not great. Strong all spice, perhaps. Reminds me of a spiced Chambly Noire or perhaps Maudite. Unibroues dark beers are not my favorites, but I can't get enough of La Fin Du Monde.