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
spiderman, when he realizes let Uncle Ben killer free!
Spiderman, when Gwen died before his very eyes!