I think I am going to be the oldest entry here (so far). The earliest comic book I remember reading was DC's Limited Collector's Edition #39 (1975) presenting the origins of the villains of the DCU. I was only 6 years old and my mom had just picked this up and brought it home. I can't remember the contents but I remember the cover of the heroes on one side facing off their counterpart villains. This has become such a famous trope on comic covers since then. And it inspired my love for the animated show Challenge of The Superfriends in 1978 as the JLA battled the Legion of Doom. Now many years later it inspires all kind of nostalgia.