A lot of films mentioned here I didn't find overly scary.
The best ones that stick out are
The Conjuring/Annabelle films (but not Annabelle comes home - the second half was more like an action in my mind)
Insidious
Paranormal Activity (agree with the PP about the kitchen fan)
The first Resident Evil film (DH is a gamer and watches all horror films, but refuses to play the game as its just too scary)
Not particularly scary, but one horror film that has stayed with me is Shuttle. Its not a very well known one.
Films I didn't rate were
Hereditary
Babadook
Blair Witch
Exorcist (but the book was terrifying)
Event Horizon (I saw it at the cinema, but it wasn't until years later that DH told me it was a horror)
I also enjoyed the Woman in Black.
When I was younger the films that scared me, but dont so much anymore were
The Omen films (the original with Gregory Peck),
Childs Play (1&2 - Didn't see 3 until much later as it was banned before I got to it, so was an adult),
Poltergeist
The Shining.