1. raiders of the lost ark
the entire opening scene when Indy is trying to get the Idol is deliberately designed to feel like it is the climax of a previous unseen episode, laying out the idea that this is a homage to the old serial adventures. the bits with the closing door, rolling boulder and being pursued down to the plane by the angry natives are just genius.
2. Terminator 2 - how can anybody not love that future war scene?
3. The Matrix - trinity fleeing across the rooftops - wow!
4. 2001 - A space Odyssey - nuff said