The whole "inspired by true events" schtick that often pops up in the opening credits of a movie, is used so often nowadays, that I rarely even pay it a second thought. But apparently, "The Rite" starring Anthony Hopkins actually WAS based in part on the real life experiences of a Catholic priest named Father Gary Thomas, who became certified to perform exorcisms after completing 40 hours of study at the Vatican. It was during this time that he met journalist Matt Baglio, author of "The Rite: The Making of a Modern Exorcist," which inspired the movie.
Despite your feelings on the movie, Tom Foreman posted a very interesting article/interview with Father Thomas, who discusses his feelings on the film as well as his opinions on other exorcism films (ie: 1973's "The Exorcist) and the true life exorcism process. The full video and interview can be found at CNN.com and is definitely worth a look.