Kurt Busiek's Astro City is one of the better alternative takes on The Justice League, and it's pretty awesome in its own right. It combines the "realistic superhero" trend started by Watchmen with the optimism of the Silver Age.
The Samaritan, Astro City's Superman analogue, is just as big a Boy Scout as the DC version, but there the similarity ends. The Confessor (Batman) is both a priest and a vampire. Winged Victory, the top female hero, is based around Greek mythology and is accused of being a feminist cult leader (hmmm... Who coukd that be?)
It's mature in the best sense of the word, and it would make a great HBO series.