Action Comics #1, the Holy Grail of comics, which contains the first appearance of Superman.
Skirball Cultural Center's new exhibit "Zap! Pow! Bam! The Superhero: The Golden Age of Comic Books, 1938-1950" features a mind-blowing collection of superhero and comic book rarities, including the first sketch of the Joker, the earliest known sketch of Superman, plus a copy of Action Comics #1 which contains the first appearance of Superman. Read more in Gendy Alimurung's "Jewish Boys and Comic Books."