I'm thinking Sarah Connor in Terminator 2. Ellen Ripley in Aliens. Women who not only kick ass, but actually have the physique, character and demeanor to make it believable. And rather than wasting time playing out some hackneyed love story, they're like 'I don't have time for that shit' and actually spend their time doing what is necessary to survive. Somewhat decent examples (though not as good as the above) would be Trinity in the Matrix and Selene in Underworld. But I don't like the emphasis on their love interests.
Angelina Jolie kicking anyone's ass is not believable; not only because of her physique but also because the characters she portrays in movies with fighting are ridiculous and trite IMO. Same with Uma Thurman, Cameron Diaz, Michelle Pfeiffer, Lucy Liu, Pam Grier, etc
Here is an image of what I have in mind, hopefully worth a thousand words.
Fighting a super-strong shape-shifting robot from the future is a crazy plot, yet Sarah Connor is one of the most believable and memorable characters in sci fi film (the T2 version of Sarah Connor, not the T1 version). It's not just the appearance; the character, the actions and reactions, the demeanor--together they make a convincing impression that if I met this character in real life she could and would --if she felt it necessary-- surely beat nearly any man unconscious, using her combination of physical toughness, pirate-like resourcefulness, and willpower bordering on pyschotic. She even looks like some people I've seen in documentaries about the FARC, not some former runway model who decided to take up a career in film running around in skimpy outfits and bending down to distract the bad guys.
Any other ideas for female characters who are actually believable as total badasses?