Jacob's Ladder - it feels like a waking nightmare; the "shiver" special effect is quite disturbing

Hereditary - a certain death is not shown on camera, but its after effects are horrifying

Requiem for a Dream - Don't do opiates or speed, kids.

The Ring - The premise is silly and dated ("Watch a spooky videotape and you'll die seven days later"), but the visuals are unsettling, and Naomi Watts does a great job of selling the growing fear of a rational woman being pursued by a malevolent spirit.