Gina Torres is well-known in science-fiction circles as a versatile character actress. She has been Cleopatra on Xena, a freelance assassin on Alias, an evil god bent on enslaving humanity on Angel, and a pirate queen on Hercules, among others. Her most well-beloved role, though, was as first mate Zoë Washburne on Joss Whedon's cult classic Firefly.
Of course, a geek pedigree isn't a good enough reason to hand her one of the most famous super-heroines of all time. But combined with the following, she's the perfect fit.