Any of the Disney Pixar movies. The Incredibles, Bolt, either of the Toy Story movies, Cars.
Journey to the Center of the Earth is fun for kids, especially if you get the 3D version. Yesterday my boys watched Treasure Planet and loved it.
We have a DVD with all of the episodes of Walking with Dinosaurs. I don’t think it was originally intended for kids, but my kids love it. It’s not too gory or scary. We also have a DVD of an IMAX movie about ocean life—can’t remember the title, but it’s narrated by Johnny Depp and that chick from Titanic. The kids love that one too.
He might also like Underdog, Hotel for Dogs, Zathura, Jumanji, The Chronicals of Narnia, or Harry Potter (the more recent Harry Potters might be too intense for a six year old, but that’s your call).
You can even go old school with the original Star Wars movies or something like The Princess Bride. Have fun!