Ross Douthat once said the most shocking thing you can say to an atheist/agnostic is not that you believe in God, but rather, that you believe in demons. On his weblog, he uses the thought to introduce three books on the subject.
M.Scott Peck wrote two of them. He broached the idea in People of the Lie, his study of evil. The second is his final book A Glimpse of the Devil. I was so fascinated by People I had to pick up longtime Vatican insider Malachi Martin's book Hostage of the Devil, which absolutely makes the worst bedtime reading imaginable. Martin's accounts of real-life exorcisms are anything but Hollywood.
Peck's early account was far less graphic, but still chilling. He apparently decided to study exorcisms scientifically from his perch as a psychiatrist. The new book is the result. If anyone has read it, I'd be interested in feedback. I'm going to give in to the impulse to buy it soon.