DH and I don't have any kids together so I can only tell you what we, two little kids at heart, watch before going. Number one choice is CARS. I didn't like the movie until after I went to Carsland and when I watched it afterwards I couldn't believe how incredible the theming was. It feels like you are right smack dab in the movie.
Other favorites to watch over the next couple of months while we wait include (and in no particular order):
It's a Bug's Life
Peter Pan
Dumbo
Pinocchio
Snow White
Winnie the Pooh
Little Mermaid
Princess and the Frog
Sleeping Beauty
not a complete list, but it's the ones I know we have lined up already to watch. I'm hoping we can go see Tomorrowland some time before we go too.