I really scenes where people choose to take heroic last stands, especially if they represent a morality upgrade. I'll give 100 for the first 10 good suggestions (even if I've seen it, as long as it's not one of the examples). 50 per after that until I close it.
I've included movie clips because they're easiest, TV and books are also acceptable.
Guardians of the Galaxy: I have a plan https://www.youtube.com/watch?v=O5qPifYpeOE
Serenity: I am to misbehave https://www.youtube.com/watch?v=1VR3Av9qfZc
Gettysburg: Bayonet charge https://www.youtube.com/watch?v=ZL-5uyp44WA
Note I've already checked TVTropes and no trope quite cuts this quite at the joints.
If you're okay with visual novels, I'm tempted to suggest Fate/stay night here. Or, for an alternate perhaps-more-approachable lens into it if a large visual novel would be too difficult/intimidating to get into, Ufotable's Fate/stay night [Unlimited Blade Works] anime, which adapts at least many of the heroic last stands from Fate/stay night even if not anywhere near all of them.