There have been many members of this team throughout the years, but a few superheroes have remained constant. The first members of the League (often called its founding members) are Superman, Batman, Wonder Woman, Flash, Green Lantern, Aquaman, and Martian Manhunter. Others that have been important members are Hawkman, Hawkgirl, Green Arrow, and Black Canary.
In the comics, The Justice League (sometimes abbreviated as JL) first appeared in The Brave and the Bold series in 1960. Versions of the team went under various names, such as Justice League of America and Justice League International.
In the television world, the Justice League was featured in two of DC/WB's most successful series. Justice League aired from 2001 to 2004 and Justice League Unlimited ran from 2004 to 2006. The former featured all of the founding members (although Aquaman was not an official member), and the latter had an expanded cast of a superheroes.
The TV show Smallville also has established its own version of the JL. Although it has not been given the title outright, a team of superheroes have banded together on many occasions to fight crime in Metropolis and beyond. So far, members featured in the show include Clark (Superman), Green arrow, Black Canary, Impulse (younger version of Flash), Cyborg, Martian Manhunter, and Hawkman. A two-part episode also featured members of the Justice Society teaming up with the League (Dr. Fate, Stargirl, and Sandman).
It was rumored that a film was going to be made based on the Justice League, but that project was scrapped in 2008. WB (the company that makes DC films) is instead focusing on its individual movie franchises (Batman, Green Lantern, Superman, and in the near future, Wonder Woman and Flash).
The Justice League is an essential part of the DC superhero world, and includes some of fans' favorite superheroes in all history. Hopefully DC will continue to produce media that stars the Justice League for those of us who can't get enough of the team.
If you want to read more about superheroes, click on the following link: Superhero Legacy