Daniel Ballou of Ballou Projects has this gallery of images for the Who's There Chair, a chair specifically designed to let you 'lock' any door Hollywood-movie style.
In the movies, jamming a chair under the doorknob can keep a threat away. That idea seldom works in reality. This chair plays on that Hollywood icon of defense, while making it functional. The back structure is steel and has leveling feet (like an extension ladder). A notch in the backrest is at the perfect height to interface with a doorknob, and rubber grips on the feet keep it in place.
Daniel is actually quite a creative mastermind: check out some of his other projects.