Personally, I dislike Christmas Tauntauns for some odd reason. I respect the people who made it for making a fan film, but I really didn’t think it deserve the George Lucas Award for best fan film.
However, my favorite fan films are:
To Know a Jedi
Troops
Revalations
Who’s on First
Star Wars Gangsta Rap
Mod Edit: the Star Wars Fan Films / Shorts - a general discussion thread may also be of interest.