Superman,Batman,Wonderwoman...look to some of childhood's most popular Halloween costumes for group ideas. Consider it a reunion of sorts where everyone gets to dress as his or her favorite superhero and then meet up to create a power-filled posse ready to save the world.
Keep a list of superheroes and mark off each one as they are chosen to avoid repeats.
Make homemade superhero costumes. Try tights, bathing suits and fabric capes with iron-on appliqués.
For an adults-only group, have an equal number of guys and girls to create superhero couples. Superman and Wonderwoman would make a perfect match, don't you think?