"Plan 9 From Outer Space" It was so ridiculous, but a cult classic! This was Bela Lugosi's last film, and he died before it was complete. The later scenes were performed by another actor covering his face from the nose down.
I like the old sinbad movies
Aliens land and end up leaving because we aren't ready to meet them.
This is a hard one, Soylent Green and Fahrenheit 451 come to mind. Favorite? I don't know but definitely a prediction of things to come.
I love anything that Ray Harryhausen was involved with! The skeleton army from Jason and the Argonauts freaked me out as a kid.
Oh just about anything that was joked on by mystery science theater. I loved those guys with their silly comments. Especially the crow