9. Secret Six #1
It's hard enough making one villain the star of your comic, let alone multiple. While the obvious argument against this statement is Suicide Squad, once John Ostrander had left that book back in 1991, it was cancelled and, inspite of a few failed reboot attempts, wouldn't return to prominence until 2011. In the interim, the idea of criminal teams would become an affectation of the larger DC universe, something referred to but seldom seem unless as antagonists.
Then came Infinite Crisis and a mini-series called Villains United, a book that pitted the last holdouts from an attempt to unify all the bad guys in the DC universe into a single society. The book was created by Gail Simone and Dale Eaglesham and was a highlight of the crossover. The creators took laughable villains like Cat Man and made them as dangerous, exciting and enjoyable as any of the company's top tier heroes.
Following a second mini-series and a slight change to the team's line-up, a new ongoing title launched in 2008, giving readers what they had been clamouring for since Infinite Crisis. The first issue told us why we should care about these characters, what made them so different and gave us a terrifying new villain and central mystery in the process.