Even though this whole list is a shameless ploy to plug "The Orphanage", it's still a pretty tight grouping. I also have no qualms with plugging "The Orphanage". That was a great movie and I will fight anyone who disagrees.
1. The Uninvited (1944)
2. Kuroneko (1968)/ Onibaba (1964)
3. The Haunting (1963)
4. The Innocents (1961)
5. The Changeling (1979)
See it here
Del Toro put together a pretty good list, although "The House on Haunted Hill" seemed to mysteriously be neglected. Oh, and "Poltergeist". Wait, that's my list... All this Guillermo talk made me giddy and confused!
Back on track! Thoughts? Feelings? Best ghosty film? And don't say "Ghost". The scariest thing in that movie is Demi Moore's hair.