Hmm.. I don't know if there is one that is the best, but these are some of my favorites.
Bladerunner when Roy Batty dies. He has this amazing monologue: "I've seen things you people wouldn't believe. Attack ships on fire off the shoulder of Orion. I watched C-beams glitter in the dark near the Tannhauser gate. All those moments will be lost in time, like tears in rain. Time to die."
Empire of the Sun: When Jim is standing on the roof of one of the buildings in the camp, and the American pilots arrive and start dropping the bombs, and he sees one of the pilots go by almost and slow motion and give him the thumbs up

I LOVE that!
True Romance: The big shoot out scene.
Dead Man: The shootout between Johnny Depp and Lance Henrickson.
Aliens: When Ripley gets into the power suit and starts kicking some alien ass. "Get away from her you BITCH!" Hehe.
Black Hawk Down: Most of the movie was one big climax IMO

So much kept happening! Go Delta Force!!
There are just too many movies to mention really
