I first saw The Exorcist around 1977 - 78, Alien in 1979, and Night of the Living Dead around 1980. All of them scared the shit out of me at that age.
Nothing else has really scared me since. There were a bunch of other horror films from the late 70s, early 80s such as the original version of The Omen (1976), The Fury (1978) and Scanners (1981). Those were mildly scary, but I saw them later, not in the original theatrical release.
Nothing released now can possibly scare me.