10. The Late 1970s - Return Of The Batman
In real terms, Return Of The Batman was never really intended to be a full movie - it was the script that Michael Uslan used to convince everyone that Batman could be in movies. It was, in effect, the script that made Batman movies, so it deserves its position as a key-stone.
As Uslan sought to make his Batman, Hollywood didn't share his enthusiasm and he repeatedly came up against brickwalls built on the back of Adam West and his campy version of the character, as Uslan said himself, studios saw Batman as "a pot-bellied funny guy with Pows, Zaps, and Whams." Silliness in other words and even when he showed them the comics that defied that image, they didn't get it.
Luckily Tim Burton did and he became Uslan's most useful ally, as he sat down and worked on a script called Return Of The Batman in the late 1970s to try and whip up some interest. And fundamentally he wanted it to be used to educate studios and executives on his and Uslan's vision for returning Batman to his origin.
It's a shame we've never even seen the storyboards, but whatever the shape of the movie, it worked and Batman 1989 was borne out of it.