The Blair Witch Project

The 1999 film that invented viral marketing and proved that what you don't see is infinitely more terrifying than what you do. Three film students vanish in the Maryland woods, and their recovered footage shows a slow descent into primal fear. The bundle of sticks, the corner scene, Heather's tearful confession into the camera — none of it relies on special effects. It cost $60,000 to make and grossed $248 million. Hollywood has been chasing that ratio ever since.