Here's #42! Click here for the master list!
Amazing Spider-Man #42
As far as I can tell, this issue is the easy choice for this number, with the first full appearance of Mary Jane Watson in one of the most famous panels in comic book history ("Face it Tiger you just hit the jackpot" or whatever the term is).
It it is striking how many notable issues took place so soon into John Romita's run on Amazing Spider-Man, it is almost as though Stan Lee knew the changeover would be dramatic going from Ditko to a new artist, so he packed these early issues with as many "big" moments as possible.
Within a year's worth of comics, the Green Goblin's identity was revealed, Mary Jane Watson, The Rhino and the Kingpin were introduced and Spider-Man famously gave up his identity.
That's some impressive stuff, huh?
Anyhow, other notable #42s...I dunno...Kirby/Lee, Moore and Gaiman all had good 42nd issues.
Any ones I'm not thinking of?