The Exorcist is STILL the bar to beat, even 45 years after its first absolutely terrifying release, and remains just as horrible to watch right now as it did back then too.
Telling the story of a young girl that starts acting strangely, and no, I don't mean teenage tantrums or arguing with her parents, but speaking in tongues and f**king levitating of all things - her mother rightly seeks medical help before enlisting the help of a priest. Turns out, she's possessed by some creepy demons, and the church is the only one that can save her immortal soul.
Featuring some of the gnarliest practical film effects that still stand up incredibly today, The Exorcist is both an excellently made film with a gripping story, and a bloody terrifying watch. Now don't go playing with any Ouija boards, if you haven't been told enough.