Great, 50s sci-fi movie poster-ish cover!
The story: "The 'I' Who Defeated the Justice League!" by Gardner Fox, Mike Sekowsky, and Bernard Sachs. An inter-galactic being simply named "I" sends anonymous letters to members of the JLA to draw them out and defeat them, since he discovers their success as a team is draining his life force(huh?).
Snapper Carr figures out(yeah, ahead of Batman) that if they use the handy Amazo, residing in their sanctuary's trophy room, they can overload "I" and defeat him. Ginchy!
Roll Call: Superman, Batman, Wonder Woman, Aquaman, Flash, Green Lantern, Martian Manhunter, Green Arrow, The Atom
Notable Moments: There's a giant full-page illustration(which Sekowsky didn't do much) of the JLA beating the circuits out of Amazo, which is fun.
Aquaman gets a fairly big role in this story. I'm always happy about that.