The Changeling (1980) This is a really entertaining and truly scary horror movie, a great one to watch late at night. It was recommended to me by a good friend who is also a movie buff but not into horror at all, so I was skeptical going into it but really loved it. George C Scott gives an awesome performance as always. Not a lot of cheese or gore like most of the movies I recommend but just a really good horror movie with great atmosphere that sticks with you. Trivia: The movie is based on events which supposedly took place at a house in Denver, Colorado, in the 1960s. The Chessman Park neighborhood in the movie is a reference to Cheesman Park in Denver, where the original haunting transpired.
If you enjoy this one you should also check out The Hand (1981) with Michael Cain.