Superheroes, edited by John Varley and Ricia Mainhardt, is a big ol' anthology of superhero-related stories from various SF writers. Shocking, eh?
Essentially none of these are straight-up superhero stories, which is just as well, as I have difficulty envisioning pure superhero stories working well in a written-only form. Instead, they're stories that take an angle of superhero mythology and play with it. There are a bunch of stories that explore the relationship between law enforcement and superheroes; several that touch on the symbiotic relationship between superheroes and supervillains; a couple that intersect superheroes with history and mythology; and so on. Most of the stories are good, but with twenty-six stories in the anthology, there's a certain amount of repetition.
The highlights of the book are probably Lawrence Watt-Evans' "One of the Boys", which explores what it really means for a Superman-figure to be an alien; John Varley's "Truth, Justice, and the Politically Correct Socialist Path", which imagines a Superman-figure landing in Soviet Russia and embracing heroically the political ideals of his new country; and Roger Zelazny's "The Long Crawl of Hugh Glass", which barely seems to be a superhero story at all.
Overall, Superheroes is a nice, fluffy anthology that's original enough to be an unguilty pleasure. It could probably stand to be a third shorter than it is, but it's not painfully overlong or anything. This would probably be a great airplane book.