Scariest movies for me as a kid-young adult which no longer scare me (but are still enjoyable) are:
Halloween 1
The Howling
Friday the 13th 1
Alien
American Werewolf in London
The Fog
The Amityville Horror
Scariest movie for me as a kid-young adult which still scares or creeps me out today are:
The Exorcist (self inflicted crucifix to the female groin while yelling F-me is still disturbing today, back when it came out it was all kinds of crazy, man was that movie ahead, advanced, whatever you want to call it, for its time)
Race with the Devil
Scariest movie for me as an adult are:
The Strangers
Paranormal Activity
Blair Witch Project
The Ring
In that order.