Justice League of America #16

Five of the Justice League's greatest heroes — Martian Manhunter, Green Lantern, Aquaman, The Flash, Wonder Woman, Green Arrow, and the Atom — are each trapped inside giant translucent spheres, struggling against their glassy prisons while a mysterious winged villain looms near an alien structure in the background. Murphy Anderson's cover for this December 1962 issue sells the premise of "The Cavern of Deadly Spheres!" with real visual punch, the heroes' helplessness rendered all the more striking against that eerie purple cavern landscape. It's a wonderfully imaginative snapshot of early-'60s DC storytelling at its most inventive.