I think most horror fans love a good exorcism. I mean, scary is always somewhat related to reality, right? And what's scarier than something that still looks human but certainly doesn't act human? Nothing. That's the scariest thing ever.
Or it can be the worst thing ever. Last night my roommate and I watch Exorcismus (2010). It's a surprisingly well shot movie that makes an attempt to be something more than your average horror film. (cough, The Rite, cough) But seriously, when your daughter levitates three feet off the floor while unconscious and your entire family is witness to it, you call a priest and do what he says. When he says "don't let her be alone with anyone." DON'T LET HER BE ALONE WITH ANYONE.
I'm bringing up Exorcismus as a very well intentioned but very flawed film. There are, on the other hand, a great many other exorcism films that are damn good. In my opinion they are....
The Exorcist (1973)
If there was ever an upside to exorcism it's Tim Burton's Beetlejuice.But it involves "bio-exorcism" aka getting rid of the living. Bureaucracy does exist in the afterlife, but thankfully it's still funny.
The Exorcism of Emily Rose (2005)
This one is like a mix of an exorcism movie and an episode of Law & Order. Half of the film depicts the titular Emily's exorcism and the other half the trial of Father Moore who performed the exorcism. It's super creepy and an interesting examination of the psychosis involved with believing oneself to be possessed.
The Last Exorcism (2010)
I really liked this movie up until the last 10 minutes. then it just got stupid. Really stupid. Do everything in the first 80 minutes, then do the opposite of the last 10 minutes.