That's easy. There really is only one D&D movie.
Star Wars. Or "A New Hope".
Not only was it out at the same time (more or less) I discovered D&D. It became so much a part of my experiences as a kid that is hard to tease out where one influence begins and the other ends.
This movie has: A boy who would be the hero, a swashbuckling rogue, a princess to rescue, a wise old man/wizard/jedi, an evil warrior, an impenetrable fortress, magic, fights, side-kicks, monsters, sword fights and epic battle. Everything here IS D&D. They even meet the rogue in a bar!
Yes this another retelling of the monomyth or The Hero with a 1,000 Faces. That's why it works so well.
If you have never watched the original trailer, watch it. It gives you an idea of what Star Wars was in the late 70s, before all the toys and baggage.
This is also one of the reasons I like the d20 Star Wars game over the West End Games d6 one. To me Star Wars and D&D are the same.