19. The Dark Knight Returns
So, what exactly is The Dark Knight Returns? Well, the story – written and pencilled by Frank Miller – focuses on a 55 year old retired Batman and his decision to head back into action alongside a new Robin called Carrie Kelly.
After The Joker snaps his own neck to incriminate Batman for his murder, the now government allied Superman is sent into Gotham to deal with the Caped Crusader as they also view the city – which has been deemed the safest in the US due to a nuclear war – as an embarrassment. Batman bests Superman in combat, but fakes his death in order to better fight crime. While not a direct adaptation, there are clearly a lot of story points here they could take and meld into a contemporary and interesting film featuring the two heroes.