Holy mackerel. Do you have other favourites? I’m a fan of “Rosemary’s Baby”, but it’s not like “Black Sunday”. Neither is “The Exorcist”, although both are well done, with some of the scenes in “The Exorcist” poorly executed, which may have been due to the technology of the day. Still.
I was looking to see if YouTube had the complete “Race with the Devil” (1975), but it doesn’t look like they do. However, Devil’s Rain wasn’t too bad. Not nearly as scary as Black Sunday. Has a lot of familiar faces.
The Devil’s Rain (1975)
http://www.youtube.com/watch?v=BsbpN9wXf6k
The Sentinel
(some R-rated scenes and language)
http://www.youtube.com/watch?v=CMi48iyKwVY
The Texas Chainsaw Massacre (1974)
(incredibly scary)
http://www.youtube.com/watch?v=fKmXwtODLHM&feature=fvwrel
Then I think you might really like The Sentinel, linked above.
The Omen 1976 Full Movie
http://www.youtube.com/watch?v=Ro53ZUm69PY&feature=related