1. Racing Flags
With a variety of plain coloured flags to choose from, the racing flags make fantastic capes for various superheroes and characters. Here's a few ideas:
Green (Start): Robin Hood, Green Lantern, Green Hornet, Green Goblin
Yellow (Danger): Robin
Red (Stop): Superman, Supergirl, Thor, King or Queen, Mighty Mouse
Blue (Move to Outside): Captain America, Wonder Woman, vintage Batman, Underdog, Wizard
White (Final Lap): Storm, Good Witch, Elvis
Black (Penalty): Witch, Warlock, Vampire, Grim Reaper, Batman
2. St. George's Cross, Flag of England
St. George's Cross is as a perfect cape for a knight costume. And it even has some authenticity, variants of the cross used throughout history to adorn knights of the Byzantine Empire, France and England. But remember: if you're going to wear a national or provincial flag, be sure to treat it with respect!
3. Jolly Roger
The pirate flags, also known as Jolly Rogers, come in a variety of designs, the most common being variants of the skull and crossbones. They are ideal, of course, for pirate capes, and could be used for Grim Reaper costumes.
4. Flag of Norway
Why not use the flag of Norway for your Viking persona? Other Scandinavian flags could also work, such as Denmark, Sweden or Iceland. And there is a historic Viking raven banner as well, although it is much harder to come across.
5. Rainbow Flag
I have seen the Rainbow Flag, or Pride Flag, worn as a cape more than any other flag. Usually it is worn at Pride Festivals, but I have also known it to be used as a costume piece for queer superhero characters. And recently, a customer purchased the flag for his double rainbow costume!