Let's start old school -Wonder Woman!
She's the epitome of the kick ass heroine. IMO she isn't given her due. Superman and Batman like to hog the spotlight, but she's a true original. Immortal and gorgeous, she decides to leave her frolicking on Paradise Island hidden deep in the Bermuda Triangle to protect humanity! Oh yeah, and like the little mermaid - she saves the handsome man from certain death.
Superpowers aside, Diana Prince is a complex character with a wicked lasso arm. She has to balance her secret identity with her womanly desires, and most of the time her womanly desires lose out. But Wonder Woman was just one of the early character incarnations in a nice string of kick ass heroines in popular fiction.
Xena, Lois Lane (the original not the 50s disaster), Charlie's Angels, and of course Buffy Summers, have all contributed to the elevation of the female character from victim, girlfriend/wife, mother status to a new level of authority in fiction.
To paraphrase Joss Whedon's famous point about why Buffy was small and blonde, he was tired of seeing the little blonde in horror movies running and screaming for her life only to end up hacked to pieces in some dark alley.
He created Buffy to lure the evil creature out - stop - turn around - and beat said evil creature to death with its own arm. Regardless of how I feel about Buffy's overall development or how I'm totally on the team that says Bella and Edward who? Buffy and Angel did it first! Buffy is the perfect example of how kick ass heroines have come a long way and can dominate.
It's no longer a given that the female protagonist is going to be relegated to running with a broken heel, screaming behind the macho hero. Nowadays, audiences are kept guessing as to whether or not she is going to turn around, pull a gun, and blow the bad guy's head off. And I for one love that.
Go girl power!