Well, this is a poll laden with spoilers, isn't it?
I second Blade Runner and raise you Serenity. Honestly, either death of a major character, but the beautiful, stoic conversation between Mal and Zoe? I wanted to cry, and I didn't know the characters as well as a lot of other people.
"Now everyone was giving her that kind of look UFOlogists get when they suddenly say, 'Hey, if you shade your eyes you can see it is just a flock of geese after all.'"
"You can't erase icing."
"I can't believe it doesn't work! I found it on the internet, man!"