I definitely can't choose, but here are some to put into consideration...
WARNING: Contains spoilers. Don't read them if you haven't seen the films.
1. 2001: A Space Odyssey - HAL 9000's Death
How amazing was this scene? Well, the whole movie is amazing, but this is just outstanding. HAL 9000, the super computer used to regulate and control every function on the spaceship, has detected a failure in the ship despite it working fine. The two conscious members on board debate on whether or not HAL can be faulty, as no HAL computer has ever had a single error. HAL, worried about being shut off, like any intelligent "being", fights for "his" survival by killing everyone on the ship outside of David, who sets his sights on literally taking out the memory chips from HAL's terminal. The emotionless voice of HAL tries to convince Dave to "calm down and take a stress pill", but starts to worry as Dave does not stop. Eventually, the artificially intelligent computer begins to BEG David to spare it. As Dave starts taking the mind apart, HAL, still emotionless, claims he "can feel it". Eventually, HAL is reduced to a mumbling, slow, childlike mindset, stating that its creator has taught it a song. Would Dave like to hear it? Well, Dave, who feels sorry for the computer, agrees to hear it. HAL, slowing down more and more with every moment, sings "Daisy...daisy...give me your answer, do. I'm half crazy, all for the love of you. It won't be a stylish marriage. I can't afford a carriage. But you'll look sweet...upon the seat...of a...bi...cy..cle...built.....for.....two...." With that, HAL is dead.
2. Dr. Strangelove or: How I Learned to Stop Worrying and Love the Bomb - We'll Meet Again
Simply put, if you've seen this film, the very end where the entire world is being destroyed due to the Doomsday Device and nuclear fallout, set to the song "We'll Meet Again" by Vera Lynn. Haunting, yet funny at the same time, which is what the entire movie goes for.
3. Reservoir Dogs - Like A Virgin
This entire opening sequence, with its four or five conversations going on, is just beyond hilarious. Tarantino's character, Mr. Brown, is adamant that the song "Like a Virgin" is all about a girl who's being fucked so hard that it hurts her just like it did the first time. Joe Cabbot, the leader of the group, tries to figure out who "Toby" is when he looks in an old address book. Mr. Pink debates on whether or not he should tip, because as he states, "tipping is for the birds". Hilarious.
4. Star Wars: Episode V - The Empire Strikes Back
How can you make a list of the best scenes in cinema history and not mention "the reveal"? Lol. Even though its one of the most often botched quotes in history, and he in fact says "No, I am your father" instead of "Luke, I am your father", this scene was so huge that it transcended the film itself and has become a part of common knowledge pop culture. The same goes for "Bond, James Bond." If you run into someone who has never heard the line before, they must be living under a rock.
5. The Usual Suspects - The Greatest Trick the Devil Ever Pulled
Keyser Soze revealed. Nuff said.
You know what...I could do this all day, lol. If you're interested in more, PM me, or check my MySpace page under my profile here. I've got a few blogs up about "best movie quotes" and such.