So apparently, along with the X-Men, Joss Whedon would also like to do a Dark Knight crossover with our erstwhile vampire slayer.

As for his ultimate comic book story, Whedon said he has long dreamed of a Buffy/Batman crossover and pictures the two standing on a darkened rooftop.
Buffy says to the Dark Knight: “That’s it? It’s just the costume? No bat powers? ‘Cause I know people with bat powers.”