2001 A Space Odyssey, the greatest leap in FX ever in movies, even bigger then King Kong in it's day. Shots of space still don't look as good.
Das Boot, easily the best use of surround sound, the standard everybody should try to attain to.
Apocalypse Now, one of the few that makes you watch it. Gripping at all levels.
Full Metal Jacket, My bootcamp in 45 minutes ...This is my rifle, there are many others like it but this one is mine. Good night Chesty wherever you are.
The Bridge on the River Kwai, A classic tale of men overcomming all obsticles to do the right thing.
Those are just 5. I can do 15 more that are equally deserving to be a top movie depending on what mood I'm in.