Donnie Darko stands out for me. The movie either hit for you, or it didn't. It was also a good metric for me back in my youth to gauge how arrogant any one of my friends was if they were so up their own ass that they were incapable of appreciating it. And I mean a really good metric.
Honorable mention to Butterfly Effect. (as cheaply executed as it was, and as dated as the cinematography was, it was still able to hit)
That is in the same vein as Donnie Darko-- these could be life-changing movies if viewed at the appropriate time in your development, depending on your background and life story.