Citizen Kane
This film is pretty controversial in the film world. Some say that the twist was boring and an easy out. Others argue that it goes much deeper than what's presented on the surface.
Rosebud
The plot point is centered around a mysterious "Rosebud." No one knows what, or who, it is. At the end, its revealed that Rosebud was Citizen Kane's childhood sled that he had kept for his entire life. Of course, a sled isn't wild, but it was supposed to humanize the otherwise cruel main character.