A Muppet Family Christmas (1987)
(FYI: Because of rights issues, in the United States three full songs and two partial songs have been cut from all video releases. Don't believe anyone who tells you this doesn't impact the quality of the special; there are plot points in those songs! I found a full copy on YouTube. )
The special plays out like a fantastic extra-long episode of The Muppet Show: loosely connected vignettes and songs, and only one human to be seen. There are ten full songs, plus a medley of eleven more. There's no new music for this special: it's all classic holiday songs, except Pass It On from Fraggle Rock, and Together at Christmas from The Christmas Toy. It's a music heavy hour, and all the songs are done beautifully. The Electric Mayhem does Jingle Bell Rock. Miss Piggy sings Home for the Holidays. The cast of Sesame Street sing Deck the Halls.
Oh, did I mention that this special is particularly significant for bringing the far flung branches of the Muppet family together for the holiday? Muppets, Sesame Street, Muppet Babies, and Fraggles all put in an appearance.
You'll appreciate this special more and more for each of these characters you're familiar with, although I think everyone can find a moment that touches your heart. If you're a Muppet fan, though, you'll love when the characters start interacting across groups: Rowlf and Sprocket, Ernie and Bert talk to Doc, Kermit and Robin sing with the Fraggles...it's like an hour-long love letter to everything the Muppets ever did under Henson. It helps that the writing is great: every character's dialogue is spot on.
If you're an even higher level of Muppet fan, you'll enjoy moments where two characters played by the same puppeteer get a moment together, like Gobo and Robin, or Animal and Cookie Monster.
I love that A Muppet Family Christmas makes me feel like all of the Muppets, Fraggles, etc. are one big crazy extended family. It closes with an 8 minute carol medley that's just full of good moments. The number of puppets in each shot is nothing short of astonishing. It's a warm, loving hour, and I think everyone should try to see it.
Not enough to convince you? Read a few more big Muppet Fans gush about this special here. (Warning, lots of spoilers in this commentary if you haven't seen it.)
Look online for the full version of A Muppet Family Christmas, or you can buy it on DVD if you're outside the USA. The cut version (which is not as good, but still has plenty of great stuff) is on Amazon, but only for lots of money.