The image of Superman's death, with Lois holding his body, the day a Superman died was a very powerful and emotional image.

Joe Fixit, beaten by the Thing, and confronted by the green Hulk Robot...both fights were awesome, but 'I'm the Hulk...aren't I' awesome moment in comics

Buried Alien wins the qualifier for the Galactic Marathon, beating Quicksilver

Batman's one punch KO of Guy Gardner in JLI

the killing joke, the scene with Batman and the Joker laughing