The Exorcist (1973)

One of the most profitable horror movies ever made, this tale of an exorcism is based loosely on actual events. When young Regan (Linda Blair) starts acting odd -- levitating, speaking in tongues -- her worried mother (Ellen Burstyn) seeks medical help, only to hit a dead end. A local priest (Jason Miller), however, thinks the girl may be seized by the devil. The priest makes a request to perform an exorcism, and the church sends in an expert (Max von Sydow) to help with the difficult job.