Batman '89. It's a good movie, it's a cool movie, and uniquely Batman. Burton goes a little overboard in Returns, Schumacher never took the character seriously, and Nolan's movies are interchangeable with any run-of-the-mill crime flick. It explores the admirable fucked-upness of a psyche that would put on a Bat-suit to fight crime in the middle of the night without devolving into Nolan-esque cynicism.
Michael Keaton killed in the role, Nicholson's Joker is actually the Joker, the set designs are creative, and Batman '89's Gotham City is one creepy place. Yeah, yeah, mock it for the Prince soundtrack, but that's not as bad as Clooney's head-shaking or as distracting as Bale's Batman voice.
And I know it's blasphemous to the comic book fans, but I just always thought it was sort of genius to make the Joker the mobster murderer of Batman's parents. The Joker is Batman's ultimate foe, and that really added another dimension.