The Haunting (1963) is one of my favorites. It's more atmospheric than most horror movies, leaving a lot to the imagination. The scenes in the bedroom where they hear voices and banging on the walls creep me out. At one point the walls seem to move. The movie was directed by Robert Wise right before he did The Sound of Music. Don't bother with the re-make. Get the original.
https://en.wikipedia.org/wiki/The_Haunting_(1963_film)
Val Lewton's movies are also worth checking out. The Cat People (1942) is worth watching, as is I Walked With a Zombie (1943), speaking of zombies above. Turner Classic Movies has lots of good horror movies on in October, if you have access to that.