I almost mentioned this because it’s pretty scary, but it’s also not a very good movie. In my opinion.
I saw Alien: Romulus for the second time recently and that is a solid good movie. It’s my favorite after Alien.
Here’s a couple of oldies, but still, I think, goodies:
Strait-Jacket, with Joan Crawford. Look for Lee Majors in the opening sequence.
The Innocents, with Deborah Kerr.
Maybe they’ve lost something over the years, but I was scared for a few days after seeing them.
Night of the Living Dead (1968)
Scream and Scream Again (1970) – Some Nazi types are creating a master race that needs blood to survive.
It’s Alive (1974) – Killer baby, followed by at least 2 sequels.
God Told Me To a.k.a. Demon (1976) – Random acts of violent mayhem connect a NY cop to his mysterious past.
Alucarda (1977) – Stylish, eerie and surreal account of two girls causing blood-soaked havoc in a Christian orphanage.
Shock Waves (1977) – Some unfortunate shipwreck victims land on a remote island inhabited by a former Nazi scientist and Nazi zombie soldiers. Guess what happens?
As I understood it OP wanted scares, so I wanted to include various movies within some subgenres of horror. Horror is my favorite genre and when I got to cosmic/lovecraftian horror I felt that Color out of Space was the best adaptation of his works. If I had made a more curated list, I would change it with Annihilation for probably best cosmic horror movie.
I wanted to include something like Hereditary or Midsommar, but figured it might be too intense…
I’m with you on Romulus, easily my second favorite Alien movie.
I haven’t seen that one! It’s been on my list for a long time.
And the only version of Color Out of Space I saw was the crazy Nicholas Cage one. I’m not sure if there are any better ones. It was genuinely freaky though. Especially some of the body horror stuff.
I don’t usually watch horror but I have a Monday movie group and I’ve seen more horror offerings since we started watching as a group. I guess they make me braver.
I also sat through Mandy, and I love me some Nicholas Cage but those movies together were a bit too much crazy Nicholas Cage at once.
It’s not quite horror but I found the recent The Northman quite disturbing and scary.
That’s the one! I think best direct adaptation of Lovecraft’s works, albeit the movie has barely anything to do with the short story outside of the meteor itself.
Oh man that’s a tough one, I find it hard to quantify or even compare it too. Truly a hardcore movie IMO. But man I do love Nic Cage’s performance. And who can forget the Cheddar Goblin! 
If you feel up for it I’d also recommend Robert Eggers other films, he did a remake of Nosferatu which I thought was a good adaptation. However his first 2 films are fine works of art, Eggers keeps those true to the time they are in with the dialogue so make sure you have subtitles on! His second film, The Lighthouse, is in my top 10 list of favorite horror movies.
Indeed. My backstory on this: I was standing a lone night watch in an empty building and was bored. So I turned on the TV and it happened to be a movie that had already started. So I thought “sure, why not” and settled back to watch these two people walking through a cemetery. I had absolutely no idea what was coming. Try sleeping alone in a creaky old building after seeing that.
Agreed on The Lighthouse. I loved it.
I also really liked Nosferatu.
The only big one I haven’t seen from him is The Witch.
He’s definitely one of my favorite directors.
I tend to think of Predator more as an action movie rather than horror. What I love about threads like this is seeing what some people consider scary while others might consider tame. I’m going to throw The Changeling into the mix which is a bit tame and many people might not think it’s particular scary. There’s no gore, very little blood even, but there’s a scene where their having a seance that left me with goosebumps as a child and still left goosebumps when I rewatched it a few years ago. It’s one of my favorite ghost stories and I think it’s largely forgotten at this point.
The second time I saw it, also in theater, the audience screamed/yelled when the chestburster killed Kane - moments later after it had scrambled off the table, the audience nervous-laughed and then burst into applause.
Ah yes Psycho, of course. The scene with the detective in the house is terrifying, more so than the most famous scene, in my opinion (although the bit in that where you see the door open through the shower curtain is creepy as eff). The part where Lila is searching the house is extremely tense too. And the final reveal… wow.
As far as newer movies: Barbarian really freaked me out.
I have a ‘creepy real life circumstances while watching a scary movie’ story…
One night I had insomnia, so I gave up trying to sleep, got up and turned on the TV. I found a movie on streaming called ‘The Exorcism of Emily Rose’ and started watching in the wee hours of the morning.
In one scene, Emily, who is a college student staying in a dorm room, has a seizure in bed and her body starts contorting horribly while she’s being possessed. The camera pans to a clock on her bed stand with red digital numbers, which shows the time as 3:00 am - established in the movie as the ‘demon hour’ when possession events happen.
Which reflexively caused my eye to turn to a clock we had near the TV-- it was the exact same type of clock with red digital numbers…
…and the time was 3:00 am exactly 
that’s really genuinely creepy - I wouldn’t be able to sleep after that.
Well, I already had insomnia anyway… 
Films that can frighten without violence are on another level. Coherence (2013) is a dinner party that manages to be creepy as all get out. I have seen more frightening things, but nothing can have greater impact than to be scared when you weren’t prepared for it.
Your child swallowing an object can be more terrifying than a car accident, you just have to set up the story properly.
This was going to be my answer, but it really only worked if you saw it back then.
Why do you feel that way? I don’t feel there was anything about the movie that tied it to 1999. The actual technology they used is now out of date but the idea of people recording themselves is certainly still relevant.
The found footage angle has been done by other movies (and had been used before) but I don’t think it’s been killed by overuse.
It was the promotion leading up to it that made it hit so well. They promoted the movie by putting missing posters of the main cast in college campuses a whole ass year before the movie even came out. People were talking about the blair witch as an actual thing with zero context of there being a movie about it. Then the movie came out as found footage and played as if it was a real thing. At least during the first couple weeks people went into it with no idea if it was real or not.
Creepshow, Poltergeist, The Andromeda Strain, and Alien scared me as a kid.
As a grown up, I don’t know that I find any horror film “scary”. It’s more like “unsettling”.
A few I don’t think have been mentioned:
28 Days Later
Day of the Dead (1985)
The Crazies (2010 remake)
Midsommer
REC
The Prophecy (because maybe the only thing worse than Christopher Walken on your ass as an avenging angel of death is Satan Vigo Mortenson)