I think that Harley Quinn just might be the most popular character in comics at the moment. People just seem to love her, and she has a strong female following as well.
Harley has many different looks over the past few years and she's come a long way from her original design of a simple red and black jumpsuit. This design from the Injustice video game is definitely among my favorite.
Look for her to be released in June for $55.99