The likes of Evil Dead II and III I can't count as scary, lets face it these movies are playing for laughs. However Evil Dead has to be up in the top 5. This movie was produced at a time when the video nasty was rife but it has still managed a long term viewing lifespan unlike some films of the time eg driller killer and I spit on you grave.
I do remember The Burning and Friday the 13th producing a shiver.
For a film to be truly scary it has to disturbing consistently throughout. To many so called horror films these days are nothing but teen adventure stories with special effects.
also look at some of the japanese stuff for real scares eg The ring or grudge.
If you want to go British (sorry i`m biased) watch The descent or the Creep.