There have been a lot of computer animated movies lately that the entire family can watch. UP was released this year and will probably be available at christmas time. Movies like Toy Story would be new to the kids and get them excited about the third one coming out next year. There's also Ice Age.
I think they're also coming out with a CGI christmas carol with Jim Carrey this year. Maybe you could talk to your local theatre about getting a showing of it at your local school.
We are thinking of doing a movie night in December too, but can't show anything "Christmas" like. I thought of a winter themed movie such as Ice Age, Snow day or Snow dogs. Dont' forget the hot coco!!
Last Christmas we did the Santa Claus with the Jack Frost character. This year we're doing Wall-E since it is out at exactly the right time for us. I thought too we might do Journey to the center of the earth and get 3d glasses for all the kids. That would be a hoot....
We did Polar express the first year...it was great. Or Horton hear a Who is very holidayish...
Just go to one of the major video rental or sale web sites. You should be able to put in search criteria like rating and that you want a holiday movie.
That Shrek one that came out seemed popular, but I think it was short.
The muppets had one. That Grinch one that came out a few years ago was cute.
If you go back to the classics, there are a lot. The old Frosty the Snowman, Peanuts. My absolute favorite is Miracle on 34th Street, but that's going waaayy back. It was an oldie even when I was a kid.