Most horror movies are so bad that I would pay a lot of money to get back the time I wasted watching them. There are some really good ones that I can watch repeatedly, though.
Among my favourites are The Shining and Angel Heart.
The first horror movies I watched were the 1940s British films Dead of Night and The Rocking Horse Winner. I still watch them whenever they are broadcast. Because they are not gory, they are regarded as suitable for daytime broadcast but I still find The Rocking Horse Winner disturbing while I watch in fascination the doom of a child trying to please amiable but self-absorbed adults.
A short oldie is The Bespoke Overcoat. It is sad and funny rather than scary but the topics should scare us. If you ever wondered what the phrase "going to Hell in a handcart" originally meant (some people erroneously say "handbasket"), you will find out moments after the film starts.
There are old and new versions of the The Monkey's Paw which are both good. This story is the origin of the notion that genies grant three wishes that always turn out badly. It makes good horror, though and I like the Wishmaster movies. Actually, there is no Arabian tradition that limits djinns to three wishes and there is no necessity that they will turn out badly, Take the djinns in Aladdin for example. In the peninsula of Little Aden (I think it has been renamed since I lived nearby) in Yemen there are small rocky hills that are said to be djinns, especially near the village of Bir Fuqum, where there was even a djinn altar. It is probably no longer used since orthodox Islam spread through South Arabia in the mid-twentieth century.
A strange supernatural movie that should be a cult classic but is rarely shown is Nina Forever.
To lighten up after a binge of Halloween Horror, I recommend The Cabin in the Woods.