The twins in The Shining. "come play with us, come play with us" NO!
NoyK reminded of something else in The Thing. When they are doing the blood test thing and Russel puts the flame to The blood and all the blood jumped up and ran for cover. that scared the absolute crap out of me since the conversation between the group had done a good job of easing the tension.
In Halloween when Laurie goes to check on her friends and finds them all dead. As she's sitting down crying trying to absorb what she saw, you can see Michael Myers' mask slightly illuminated in the shadows. Great creepy stuff.
the epic Laurie chase scene from the first Halloween movie
seriously, the music, the atmosphere, the way the camera flips between Michael and Laurie while she bangs on the door to show how far he is and that he's getting closer and closer..
Everything about this scene was so great. The timing was so spot on with the music going from suspenseful to thrilling. The perfect slasher movie chase scene.
Another movie scene that is scarier and a really good jump is from Alien towards the end when the alien pops out of nowhere from the shadows to kill one of the crew members. It was unexpected and terrifying when I was a kid!
Not forgetting Jason jumping out of the lake at the end of the original Friday The 13th!