The Man himself from A Charlie Brown Christmas. I always loved all the kid's dancing animations.
A little bit of trivia I know, it's very rare to come across a copy of this special that still has the Coca-Cola billboards in the background of the opening shots. (When it originally aired, Coke was ironically the main sponsor of this special about anti-commercialism.) Also, the song that everybody designates as Charlie Brown's theme song, titled "Linus and Lucy," was originally written for and only meant to be used in this special, but it ended up catching on and being associated with the characters.
PigPen and Linus from probably the most famous special of all, A Charlie Brown Christmas. Everybody knows this special inside and out but I'm still surprised every year at just how good it is. I love how all the other kids are so hard on Charlie Brown, it crosses into an area of genuine dislike that I'm not sure would be used in a special made today.
Bert and Ernie from another one of my all-time Favorites, A Muppet Family Christmas. I understand that the unedited version is hard to come by these days due to rights issues, but the original includes a giant cast of characters from The Muppets, Sesame Street, and Fraggle Rock all together in one house. There's even actual puppet versions of the Muppet Babies and a cameo by Jim Henson.
Santa's Little Helper from the very first Simpsons episode ever, where the Simpsons rescue him from a greyhound racetrack just in time for Christmas. He's seen here thinking about his favorite subject.
This may not be from an actual special, but everybody my age remembers the holiday Fruity Pebbles commercial where Barney finally shares some of his cereal with Fred. I know quite a few people who can still recite all of the dialog, even all these years later.
Garfield and Grandma from A Garfield Christmas. This is one of my favorite specials of all time. It's surprising how genuinely funny and moving it is. I think it deserves to be added into the mix of currently aired Xmas specials.
Stinky from the Ren & StimpyShow episode "Son of Stimpy," originally titled "Stimpy's First Fart." My grandmother bought me the VHS of this special one year for Christmas. I remember thinking about how unlikely it was that a cartoon character as gross as Stimpy had never farted before.