To my earlier list let me add:
-GAUDETE! by the Mediaeval Babes, also by Steeleye Span
-IN DULCI JUBILO any traditional arrangement.

Mariah Carey's "All I want for Christmas"

bump!

"Oh Holy Night" - very few can pull this off and when they can, it can take your breath away.
"Little Drummer Boy"
"Silent Night" It's not Christmas till we go to candlelight service and sing this at the end while holding our candles. (and hoping the little twit behind me isn't tilting his candle and dropping wax on my new wool/cashmere coat -- yes, this happened).

Silent Night
Joy to the World
12 Pains of Christmas :)

Classic carols such as "O come all ye faithful", "God rest ye merry gentlemen", "Angels we have heard on high", and "Carol of the bells".

"Once in Royal David's City"

"God Rest Ye Merry Gentlemen"

"O Little Town of Bethlehem"

"Angels We Have Heard on High"

"Children, Go Where I Send Thee"


Non-religious

"I Want a Hippopotamus for Christmas"

"(You Gotta) Shop for Christmas Presents" - PHC to the tune of "Lonesome Highway".

"All I Want for Christmas" - Vince Vance and the Valiants - the original!

I like a lot of Norwegian Christmas songs. :p I'm basically too cool for words.

After decorating the tree last night with the 3 year old, I found a new appreciation for "Christmas Don't Be Late" by Alvin and the Chipmunks.

BLUE CHRISTMAS
Merry Christmas, Baby
Santa Claus Is Back In Town
All I Want for Christmas is You
Please Come Home for Christmas
Have Yourself a Merry Little Christmas
I'll Be Home for Christmas
Rockin' Around the Christmas Tree
Jingle Bell Rock
Ave Maria (Kind of an Xmas song. BUT, I ONLY like it if it is sung by a woman...)
Dance of the Sugar Plum Fairy -- from the Nutcracker

And what are your 2010 favorites? I want to add "The Snowflake Waltz" from the Nutcracker.

^ I play the entire Nutcracker suite around christmas time!

O Holy Night, Carole of the Bells, and "The 3 Tenors" Christmas album. :)

I always loved Little Drummer Boy even though a lot of peopel hate it. I foudn an excellent version by a group I love as well http://www.youtube.com/watch?v=TLqqCm9B6ro&feature=fvst

Old school: "This Christmas" ~Donny Hathaway
New school: "Merry Christmas, Happy Holidays" ~N*Sync or "All I Want for Christmas" ~TLC

Trans-Siberian Orchestra's "Christmas Eve Sarajevo" is by far my favorite. I could listen to it year round :-)