5. Paranormal Activity - "Demand It!"
Paranormal Activity might have been released in late 2009, but it had actually been languishing around for 2 years prior, having played at film festivals and basically gaining a small word of mouth. Everything changed when it landed in the hands of Steven Spielberg, who liked it so much that he made a few suggestions as to how it could be more financially successful, namely altering the ending. With his endorsement, the film was slated for a limited release, which kick-started a superb viral marketing campaign which urged viewers to "demand" the film at the end of the trailer, pledging that they would go see it if it was released in their area. Also, those who had seen limited release screenings were encouraged to tweet ecstatic reviews about it afterwards. Slowly, the film began to expand to a wide release, eventually resulting in it grossing $193 against a $15,000 budget, making it one of the most successful indies of all time.