TV: The opening scene to the first season of Justified when Marshal Raylan Givens talks Tommy Bucks into pulling first so he can be justified in shooting him in self-defense. I also love the way that decision has followed him the rest of what I have seen of the series. I'm almost through with the second season and it still keeps coming up. It's a good reminder to us all that even if you're justified in what you are doing there will be consequences you'll have to live with the rest of your life.
Movie: I would say a tie between the end of Live Free or Die Hard when John MClane shoots through his own shoulder to kill the bad guy so he can save his daughter. I love that act of sacrifice for a loved one. The tying scene is in The Outlaw Josie Wales when he is fighting the redlegs and he just keeps pulling out revolver after revolver. That and Pale Rider with his Remington 1858, I had to get one just because of that movie.
Okay, pretty much any western. There's a reason my first handgun was a single action.