Without question...no doubt...unbelievably...the scariest movie I have ever watched...
"Haunting of Hill House" made in 1963 with Julie Harris and Russ Tamblyn. NOT the piece of shit remake in 1999. It's based on the damned creepy Shirley Jackson novel.
http://www.imdb.com/title/tt0057129/
The only caveat I can give you, though, is that you must bring your imagination with you. This is NOT a passive experience, and the ghosts are only heard and never seen.
By the way, for more reading on this topic, check out this earlier thread:
http://www.tfproject.org/tfp/showthread.php?t=5412