I would include Robert N. Lee's "Finest Kind" from his 666ties stories. Otis Redding and Elvis are superheroes, but not allies. There's more about the stories in the series at Awesomedome.com.
This is the second plug I put off making because the work doesn't neatly fit in a genre, so I'm not quite sure how to tell the people who will love it that they will love it and the people who won't get it that they won't get it. This particular story may appear to be about super heroes, but it really isn't. It's a gonzo meditation on the mythical 1960s.