The silent Nosferatu features the most terrifying vampire moment as he ravages a ship.
The opening moment with Boris Karloff coming alive in The Mummy scared the you know what out of me.
That swimming pool scene in Cat People got in my head.
I couldn't stand the look on the hero's face when he kisses his girlfriend in Invasion of the Body Snatchers.
It the Terror from Beyond Space had a lethal space monster that had me covering my eyes (I was very impressionable as a child). Its loose remake as Alien had me at its mercy especially the hatching egg scene.
Carrie has the showstopper surprise in the last few frame that to this day still makes me jump.
Certainly other films had more shock value and gore but scary is special. These were just some of mine.