Here's #30! Click here for the master list!
Here it is, Norman Mingo's classic first cover appearance of Alfred E. Neuman (Neuman had many small appearances in the magazine before, but this was the classic one, and the first one where he was the focus of the cover). Neuman would go on to appear on basically every cover of Mad since, becoming a major cultural icon, so really, this was an easy choice.
That doesn't mean that there aren't a lot of good candidates out there...
Superman #30 was the first comic book appearance of Mister Mxyztplk.
X-Men #30 was the wedding of Scott Summers and Jean Grey.
Fantastic Four #30 was the first appearance of Diablo.
Amazing Spider-Man (Vol. 2) #30 was the first issue of JMS' eight-year run on the title.
Was Amazing Spider-Man (Vol. 1) #30 the first mention of the Master Planner?
Saga of Swamp Thing #30 was a particularly good issue.
Name me some more #30s, folks!
Tomorrow is #16, which is the first appearance of a character in a title with a hyphenated word in the title!