15. Lina Lamont (Jean Hagen) in 'Singin in the Rain'

This ditzy silent-screen star is about to be ruined by the advent of talking pictures, until she realizes that having ingenue Cathy (Debbie Reynolds) dub her voice isn't such a bad idea. She demands that Cathy go on doing that "and nothing else!" Her best scene: She waltzes into the studio head's office and points out that he'd be in violation of her contract if Cathy gets credit. "It would be det-ri-mental and de-le-terious to my career," she beams, happy at mastering such big words.