Kelsey Leigh (before she became the new Captain Britain) standing up to Thunderball from the Wrecking Crew to save the unconcious Captain America. This random single mom walking her kids home steps in, picks up The Shield, and gives her life to save Cap from being murdured while he's down. T-ball gave her every chance to back down and get away, but she wouldn't give Cap up to be killed.
It was inspiring.
I thought about Constantine too, but I think he's not so much brave as suicidal. He's to ornery to just give up and die, so he drinks too much, chain-smokes, and antagonizes the powerful hoping that some day he'll get what his self-loathing and guilt tell him he's got comng to him. Ironically, his desire to atone for that same guilt is what keeps him from giving in and makes him a champion
I'll still go for Kelsey. Again, she was a normal person going about her daily routine who stood up to a guy swinging a wrecking ball to save the life of someone she'd never met. Thunderball told her straight out that he admired her spirit but she had no chance against him, and to step aside or he'd beat her to death too. She didn't, and so he did. She bought Cap enough time for the other Avengers to arrive and save him, but her injuries were so severe that she died from the trauma and internal bleeding. (Brian Braddock later draws her soul into Avalon and ressurects her as the new Captain Britain.)
Superheroes face death every day, they know it. It's part of the life they lead. She was just walking her kids home from the store. When all the other civillians were running for cover, she knowingly laid down her own life rather than let a good man be murdered. Kelsey went so far beyond the call of duty that day I don't even have words for it.
Two things.
1. Namor showing up to New york always having something to do with him trying to steal Sue from Reed...he knows that Reed knows but he doesnt care
2. batman going up against Darksied with nothing more than a mother box, and a few pieces of modular armor knowing he'd get his ass beat and on top of that threatening to blow up apokolips if Darkie doesnt leave the new supergirl alone...and then on top of that refusing to let the mother box heal him cuz he's either too proud or too stupid