Alien would probably be top of my list too...but The Shining was just plain creepy, too.
My 21 year old saw The Descent and he said it was really scary. The Ring (which I’ve also never seen) was supposed to be a very disturbing movie too.
I don’t normally care for scarey movies, but I watched ‘The Ring’ with my teen boys when it came out on DVD and we all really liked it. A few gross parts, but you can close your eyes, just like I do! It’s pretty standard horoor, but it’s beautifully filmed.
I also like ‘Signs’ very much. I’ve watched that a numner of times, though I wouldn’t classify that as ‘horror.’
And I can’t take two minutes of ‘Blair Witch Project’ without wishing them all dead, immediately, LOL!
The Ring is scary and the special effects are creepy. It’s a good horror story without the gore.
The Ring was creepy but well done. The Grudge(another Japanese movie that was remade) was a crapfest imho.
In my opinion, the most frightening film on that list.
If you haven't seen it and want to, do yourself a favor and rent the "director's cut" version to watch the original (U.K.) ending which was edited for American release.