Your Favorite Movies that make you Think

An obvious answer: Requiem For A Dream

Made me think about drugs in a bad way. Dang.

A post thought to the above answer: Half Baked

It made me think about drugs in a good way. Booya.

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I agree with many of you that Eternal Sunshine of the Spotless Mind really made me think. I'm sure all of us at one point or another have wanted to "forget" about that past relationship, that friendship that ended badly, or that person you miss more than anything. We tend to focus on what went wrong rather than the amazing times we have shared with that person, or the way we have changed as people because that person was a part of our life. I think that is part of what that movie was touching upon, no matter how painful memories can be, your memories (even the painful ones) are so important in making you ...you! Heh, as you can see I am STILL thinking about this movie.

Shawshank Redemption. Made me look at freedom in an enlightened way.

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Qui-Gon Jinn: The ability to speak does not make you intelligent.

What do you mean by 'makes you think'? Think about what? Just makes you do a lot of thinking to work it out or just think about matters in general?
If it's matters in general, my favorite's a classic: To Kill A Mockingbird

Memento
Fight Club
Mulholland Drive
Matrix