All of the Hellraiser movies (some are great, some are not so great, but it's worth it to work through all of them in order). The newest was kind of a re-imagining and you can start there if you want).

The Thing - the 1982 film is a classic, but the newest one is a prequel that came decades after the original movie- I'd recommend watching both, starting with the original.

All the alien movies. Some don't consider Sci-Fi horror to be true horror, but these are essential watching. I consider it to be the best complete horror series of movies ever made.

Vampire's Kiss (Nicholas Cage) - this is truly bizarre and if you are a Nick Cage fan it should be considered required watching.

Barbarian (2022) - simultaneously mind blowing and absolutely terrifying. Probably the best horror of the past 5 years.

The Mist - and mainly just for the ending which was a total mindfuck.

Train to Busan - This is a Korean made film (with subtitles) in the zombie genre, and is absolutely riveting.

World War Z - an outstanding zombie genre movie - one of the first zombie movies to feature fast moving parkour capable zombies as opposed to the slow moving classic zombies.

American Psycho - scary because this could (and does) happen and you could be standing right next to the next American Psycho right now and not even know it.

Maximum Overdrive - doesn't get recommended a lot, but it holds up and is a great machine-uprising type of horror.

Event Horizon - propped up as SciFi Horror but this is a classic true horror just with a scifi backdrop.

I WISH there would be a modern remake of "Scanners". Scanners is great horror from decades past but it just doesn't hold up well to modern standards-it desperately needs a modern remake.