Man, that pose Green Lantern is in looks really uncomfortable. Props to Mike Sekowsky, though, for putting this much on a cover and still not make it look too crowded.
The story: "The Mystery of Spaceman X!" by Gardner Fox, Mike Sekowsky, and Bernard Sachs. An evil alien uses a giant spaceman(at left, destroying property) to absorb the energy created by giant disasters, and of course the JLA tries to stop him!
Roll Call: Superman, Batman Wonder Woman, Aquaman, Flash, Green Lantern, Martian Manhunter, Green Arrow, The Atom
Notable Moments: I really like "Spaceman X"'s design--classic early-60s space explorer togs that look like they came right from a Universal sci-fi movie.
Superman basically saves the day at the end; I'd say this was the unofficial start of when Superman and Batman started to dominate the book and almost always took a central role in any given story.