The cast of Scrubs does Charlie Brown Christmas, in their own way: (groked from squished_frog). If you are a Scrubs fan like me, this is beyond wonderful.
El Vez, the Mexican Elvis, performs "Feliz Navidad" and a couple more (watch the volume, it's loud). I saw El Vez in San Jose in a holiday show many years ago and it was fantastic.
"Raging Rudolph", the Scorcese style holiday special. Funny, in a funny-sick-funny way.
"Rudolph's Bloody New Year" aka "The Reinfather", the sequel. This one is more "Godfather" than "Rankin-Bass".
"Hey Ya, Charlie Brown" (Outkast audio, CBC video). Cute, but after about 45 seconds, you've seen all you're going to see.
And two extra:
Beatnix, an Australian Beatles tribute band, sings "Stairway to Heaven" (grok'd from Boing Boing). It's just amazing how well it works.
Gnarls Barkley performs "Crazy" with a Star Wars orchestra. Not a holiday video, but dang cool and wonderfully, excellently nerdy.