Besides The Dark Knight Returns
, there's another Batman/Superman crossover that Snyder and Goyer should pilfer from. And, interestingly enough, DC is reprinting it this fall. That would be 1989's Dark Knight Over Metropolis
The story is a pretty trivial murder mystery that brings Batman to Metropolis. The important thing about the story is the conclusion, where Superman gives Batman Luthor's Kryptonite Ring because, and I'm quoting this from some very old memories, Superman wants the power to kill him "in the hands of the one man I can trust."