Beyond The Door
absolutely petrified me as a kid, and as a bandwagon film, and perhaps the most famous of the Exorcist ripoffs, gets good mention.
Local NY stations would run the commercial just a 10 o' clock when kids had to go to bed. And we all were affected by that nice little question that Juliet Mills gets to ask in this little scene:
Low budget, yes. But a true feeling of evil pervaded the possession scenes and made it a truly brooding and atmospheric film.
Other faves of mine:Horror High
aka "The Twisted Brain
"Tombs Of The Blind Dead
and it's sequels
Lucio Fulci's films, namely Zombie 2
and House By The CemeteryLet Sleeping Corpses Lie
aka Don't Open The WindowTales From The Crypt
and The Vault Of HorrorSuperstition
(early 80's Italian movie.)
and many many more!