One of the early, groundbreaking 'superhero' comics was Will Eisner's The Spirit, a vigilante crime fighter in the mold of Batman, though without the cape and tights. I've had Eisner and his prodigious drawing and storytelling abilities on the mind ever since seeing Eisner's New York at the Museum of Comic and Cartoon Art. (It'll be up until June 30).
There's an upload available on the web of a selection from The Spirit where he ventures to the moon with a group of convicts. The story is relatively thin but interesting in its depiction of space travel and lunar investigation. It's also gorgeously drawn, in Eisner's flowing style.
A young Jules Feiffer usually worked on The Spirit as well. So that's two legendary comics for the price of--
well, for free.
See the pages at Golden Age Comic Book Stories.