Superheroes have a new crusade these days: helping people send letters with the help of the U.S. Postal Service. A set of 20 stamps honors the creations of Marvel Comics, and include Spiderman, The Incredible Hulk, Sub-Mariner, The Thing, Captain America, the Silver Surfer, the Spider-Woman, the Invincible Iron Man, Elektra, and Wolverine. In addition, 10 of the stamps highlight covers of comic books featuring the characters.