Alpha!Church from Red vs. Blue. At the end of season 6, scarcely even willing to accept that he's an AI instead of a ghost, he goes with Washington to distract the Meta and his many AI, keeping them from killing Wash while Wash sets up an Emp to destroy all of the AI. Wash warns him that when it goes off, Church will die too. His response:
Church: When it goes off, I'll be fine. It only affects computers, remember? And I... am a motherfuckin' ghost.
While technically not an example due to surviving, Epsilon!Church later gets one just as great. Upon realizing that the containment device he chased Tex into is about to collapse, he finally sits down and discusses his painful history with Tex and allows himself to forget her (deleting her from existence) as a way to end her endless suffering. After which, he calmly sits and waits for the end after uttering the following line
Church: Okay world, do your fucking worst! 'Cause I sure as hell just did mine
General Doyle gets one in the Chorus Trilogy, destroying the city reactor, and as such taking out most of the mercenary army fighting his people.
Epsilon gets one for real at the end of season 13. With the Reds and Blues trapped in a room with Charon's forces about to breach the door, everyone gears up ready for a Last Stand. Right before the door is breached Epsilon leaves a message to his friends and others to several other people explaining that he is deconstructing himself so that the fragments he'll leave will be able to run all the enhancements in the Meta's old armor so that everyone will have a chance of surviving the fight. As he says good-bye he laments that he'll never know if his sacrifice really made a difference, but he just needs to have faith that it will be enough.
Church: Ain't that a bitch.
Ma Ti in Suburban Knights. After years of being the Butt Monkey of That Guy with the Glasses, he gives an epic rant at his poor treatment and viciously insults Malachite, having long stopped caring what happens to him. And then it turns out his ring can defeat Malachite, so he goes out in an epic Beam-O-War and saves the day.
"Somebody has to merge with it. Somebody has to keep it safe.
One from the archives of the SCP Foundation: a D-class unit, sent in with a video feed to die for recon, apparently singlehandedly fought his way to and destroyed the source of SCP-1983... despite being unarmed.
Some rare metahumans in Brennus are able to 'swan song', burning away their power (and their life) within a few minutes in order to flare their power to new heights.
RWBY: Though Pyrrha eventually loses her life, her final fight is a powerful struggle against Cinder, throwing the huge gears in Ozpin's ruined office at Cinder, landing solid hits, and once even pinning Cinder by the throat. Even with the complete powers of the Fall Maiden, Cinder actually struggles to gain the upper hand over Pyrrha and retain that advantage long enough to win. The fight strongly implies that Cinder, despite being the Big Bad, could not have defeated Pyrrha without the Fall Maiden powers. Pyrrha is a prodigy after all.