6. Batman & Judge Dredd
Batman and Judge Dredd have faced off in four crossover comic books, and I find this one especially fascinating, because Batman and Dredd are such ideologically opposed characters, and as such, a film pitting the two against one another could be amazing. Batman takes the view that under virtually no circumstances can he kill, requiring a line to separate himself from the criminals, whereas Dredd takes a more politically Conservative approach, that to mete out justice, you need get down in the gutter with the undesirables, and give them as good as they get. Though the comics take the expected arc of eventually forging a friendship between the two, their different approaches to the law could make for a darkly funny buddy cop movie of sorts, with each questioning the other's methods before they arrive at an uneasy understanding by film's end.