By original I mean, not based on any existing intellectual property. Pixar has been the absolute kings of this, I mean how people could come up with the ideas for stuff like Monsters Inc, Up, Wall-E, and Elemental blows my mind.
It's a little trickier with live-action stories because you don't have limitless CGI at your disposal, but I'll ask the question:
What are some of your favorite live-action stories/plots from movies that you feel have the most originality?