2. Justice League (And Justice League Unlimited)
This show was just genius, pure and simple.
And while the original series was indeed spectacular, it is its sequel that fans have most to be thankful for. Unlimited - apart from having one of the best cartoon intros out there - took what the first two seasons of the show started and cranked the dial all the way up to eleven, including pretty much every character to have been featured in a DC comic book and shining a light on the universe's lesser known characters without hesitation.
The show also, in no small part, presented some of the most intelligent comic book storylines to have been featured onscreen, with the Cadmus arc in particular representing a definite high-point in the series' tenure. It challenged the general conventions of the superhero genre, and presented a narrative that really questioned the political landscape of the DCU, as well as the ethical characteristics of the League itself. One such episode from the arc, Question Authority, genuinely remains in contention to be one of the best comic book storylines out there. It's that good.
There's just so much to love about Justice League. Apart from the fact that it brought together pretty much every DC Comics character in existence under one roof, its nuanced approach to storytelling went above and beyond what many thought achievable in the medium, never mind in the comics themselves.
Oh, and the pay-off of seeing Superman utterly decimate Darkseid in the show's final episode really was something to behold. Even better was the fact that the series was able to close on its own terms, but to see it end in that fashion? Amazing. Simply amazing.