2. Psycho - Psycho By Robert Bloch
Psycho was a novel? Yes, it was. Believe it or not. And the movie is apparently quite faithful to it, with some changes made by Alfred Hitchcock and Joseph Stefano, who wrote the screenplay. Is the iconic (and often parodied) shower scene in the novel? Yes, it is. Is it as memorable as the film version? Beats me, but I'm now really curious. There were sequels to the novel as well, which have nothing to do with the film sequels.