Most of my favourites have already been mentioned or will eventually surface (The Godfather, Star Wars, A Clockwork Orange, Rocky, Alien, Taxi Driver, Life of Brian...). So let's bring up the weird one: Bedknobs and Broomsticks. That movie was my childhood! Watched it so many times I broke the VHS xD
I love this movie with all my heart. I still find myself singing the songs from time to time(in spanish, because that's how I watched the movie)
And that final battle in the end with the revived armors against the nazis... It still blews my mind. No wonder it won an Oscar for Best Visual Effects
By the way, this year it's its 50th anniversary. So... Happy birthday ^^