A series of comic books that have existed in one incarnation or another from the 60s to the present.
Founding members included Batman, Superman, Wonder Woman, Flash, Green Lantern, Martian Manhunter, and Aquaman, though DC likes to re-write history and past founders have been changed to exclude Batman, Superman, and Wonder Woman, including Black Canary, Moon Maiden and Triumph instead.
There have been three main series of Justice League of America comics with many spinoffs, including international branches, rotating teams, and even a black ops league. The Justice League formula tends to be this: Popular heroes team up in the beginning, there's some internal conflict in the team, and the team separates and reconstructs with some new obscure members. As the comic goes on, the reconstructions occur more and more often, until finally the comic is full of people you don't know and it gets canned and restarted quickly.
There is also a Justice League Unlimited comic book, proving that it is possible to sell a comic book, that is based on a show, that is based on a comic book.
LITTLE KID: "Hey, is that comic book Justice League Unlimited like on Cartoon Network?"
OLDER DUDE: "No way, it's good old Justice League International with Blue Beetle and Guy Gardner."
LITTLE KID: "Blue who?"