Justice League (2001-04) & Justice League Unlimited (2004-06)
Credit: DC Comics
One of the best incarnations of America's favorite superhero team, and a show that raised a generation. Justice League started with just seven core members Flash, Batman, Wonder Woman, Green Lantern Jon Stewart, Superman, Hawkgirl and Martian Manhunter showing them as new heroes. Soon these exceptional beings became a team and family, and the protectors of Earth.
In Justice League Unlimited (JLU) the show expanded tenfold. Despite having a powerful team in the first seasons, with the season finale before the show turned to JLU where the Thangarians (Hawkgirl's alien race) the team realized that they needed more help. So they called in heroes from everywhere, heroes that were more known like Green Arrow, Aquaman, Black Canary, and Supergirl and lesser known heroes like The Question, Huntress, Booster Gold, Red Tornado and Vixen. Soon the show became less about the original seven though they were still in charge, and more about the smaller team members, showing the growth of younger heroes.