Yep. Exorcist. What more can we say? The first setup a whole new future of horror and, well, blockbusters where cinema lines became an overnight event. Star Wars would not have been as successful if it wasn't for the cinema going trend that started with this terrifying event.
As for Heretic, Beginning and Dominion... these movies should never have been made. Only Exorcist III, Legion stands out for being brave enough to play with the genre. We have Blatty to thank for that too.
So covering Exorcist, Exorcist II The heretic, Exorcist III Legion, Exorcist the Beginning and Dominion the prequel to the Exorcist.
At least the last two (Prequels) were fair background sounds. The English Patient was scarier than either movie.