The Peanuts gang and their classic, A Charlie Brown Christmas, seems the most open to mashup and light parody (see Hey Ya and SNL's clever version). I think it is because it has become part of our common pop culture heritage over the past 40 years, as special to kids as their parents and grandparents.
The latest I have come across is a 10-minute version of the ‘toon, voiced by the cast of Scrubs. It’s not just a rework, but their own dialogue done in character and it’s great, even if you don’t watch the show. J.D. plays Charlie Brown, Dr. Cox is Linus, Carla is Lucy, Turk is Schroeder, Elliott is Sally, Ted is Pigpen, among others. The mashup (does this qualify?) was reportedly made for a cast Christmas party.
And as a parting gift, my friend Steph sent me a link to The Christmas Spot, which has links to 101 classic Christmas videos and is where I found the Scrubs video. Merry Christmas everyone, and I’ll see you in a few days.