This is a special category for comics that are historically significant for reasons not connected to a specific retrospective.
1935
New Fun Comics #6 (Dr. Occult, earliest recurring original character that is still part of the DC Universe)
1938
Action Comics #1 (first Superman, and first superhero)
1939
Action Comics #13 (first supervillain)
1940
Marvel Mystery Comics #7-8-9 (first superhero crossover)
Daring Mystery Comics #6 (first Marvel story with Hitler)
Red Raven Comics #1 (first Marvel story penciled by Jack Kirby)
All-Star Comics #3 (first superhero team)
1941
Pep Comics #17 (first superhero killed off for real)
1943
Captain Marvel Adventures #22 (first serialized adventure, first supervillain team)
1945
More Fun Comics #101 (first Superboy, retroactively the first Earth-One story)
1947
World’s Finest Comics #30 (The Batcave penny)
1949
Superman #61 (Superman learns he’s an alien)
1952
Superman #76 (retroactively, first Superman and Batman from Earth-One)
1958
Action Comics #242 (First Kandor)
Adventure Comics #250 (first Silver Age Green Arrow, disputably)
Adventure Comics #252 (first Red Kryptonite… kind of)
1960
Action Comics #262 (origin of Superman’s powers revealed)
Superman #141 (Superman’s return to Krypton)
1961
Adventure Comics #283 (first Phantom Zone)
1963
Adventure Comics #304 (first superhero death)
Adventure Comics #312 (first superhero resurrection)
Superman #161 (death of the pre-Crisis Kents)
1964
Fantastic Four #22 (First “It’s clobberin’ time”)
Avengers #10 (First “Avengers Assemble”)
World’s Finest #141 (Batman’s new logo)
World’s Finest #144 (Jimmy Olsen learns Batman’s identity… really)
1966
House of Mystery #160 (first DC comic featuring Plastic Man)