This will be a fairly self-indulgent blog post. I always see "lists" of various types, and thought I would make one of one of my favorite topics of discussions, films. There's no methodology here, and no particular order to the scenes.
The Godfather-Purge Scene
At Michael's baby's baptism, he takes his oaths while his goons mow down his enemies in the streets. I love when the priest says, "Do you renounce the Devil and all his works?" and Michael says, "I do renounce them." All the while people are getting killed by Michael's henchmen. Brilliant filmmaking.
Monty Python and the Holy Grail-Socialist Peasant
King Arthur is lectured by a peasant about the proper role of government. The peasant claims that he was unaware that he even had a king. He thought he lived in an autonomous collective. "Do you see the violence inherent in the system?"
Kevin Spacey plays a very creepy serial killer killing based on the seven deadly sins. At the end, well, if you haven't seen the movie, you should watch it. But he and Brad Pitt have a memorable scene together, to put it mildly.
Rick tells Ilsa to go with Laszlo, confirming your sneaking suspicion that he is after all concerned about more than himself. Then Rick shoots the Major, but Louis refuses to turn Rick in. This prompts the line, "Louis, I think this is the beginning of a beautiful friendship," as they walk away. I do it poor justice, but it's a pretty awesome end to a pretty awesome movie.
To Kill a Mockingbird-Courtroom Speech
Atticus' amazing speech followed by the reverence given him by the blacks segregated in the crowd is one of the most amazingly powerful things I've ever seen. The line the preacher gives, "Stand up Jean Louise; Your father's passing," is just incredible.
Casablanca-Crowd singing "La Marseillaise" over top of the Nazis
Fight Club-"His name is Robert Paulson"
Reservoir Dogs-Ear Amputation Scene
Dr. Strangelove-Major Kong Riding the Bomb
Feel free to draft your own list and post it in the comments, or criticize mine.