Somebody mentioned Omega Man.... I loved that movie. Yea, it's tame to today's movies, but when I was young it creeped me out. Anthony Zerbe and his zombies coming out after dark and ole Chuck having to keep the spotlights on all night. And it wasn't even really their fault. It was government vs government and germ warfare that caused the whole thing...and Chuck represented the government that brought this own them. In a way, you could see that they were justifified in their actions, though insane they were.
I liked Planet ot the Apes too. Seeing Moses trying to escape talking monkeys was pretty scary for a kid...I didn't get all the implications as a kid, but as an adult I gained a whole new appreciation for it as I understood the meanings behind it.
Even thoough those movies were glorified B movies, the stories were much deeper than today's blockbuster action end-of-the-world movies. New ones rely on CGI and action to tell the story when it used to be the ideas behind the catastrophy that sparked the older ones.