1. Barry Allen/The Flash (Crisis on Infinite Earths #8, 1985):
Sorry if you thought Superman was going to be on the top of the list, but his death just doesn't compare to this one. Comic book historians have long considered the beginning of the Silver Age of Comic Books to be the first appearance of Barry Allen in 1956, and with "Flash of Two Worlds" in 1961, Barry also managed to be present for the start of the DC Comics Multiverse that Crisis tore down (for a while, anyway). The Silver Age had passed into the Bronze Age by 1985, but many of that age's hallmarks remained in DC's pages, and Barry was always among them, gleefully fighting crime as the Fastest Man Alive. Here, his run ends in grand fashion. Barry Allen dies not just saving a person, not just defeating a villain, not just helping his friends, but saving all of existence, literally running himself into oblivion for the good of everyone and everything, because he refused to give up. It's a symbolic passing of an age, one of the most heroic deaths in comics ever, and a moment that remained a keystone of the DC Universe until Barry finally made it back more than 20 years later. It might not be the death most remembered by non-comics readers or casual fans, and it might not be the one that got the most media coverage, but Barry's end is, for me, the most important superhero death ever.