Inspired by, xkcd: Action Movies, of course.
Chuck Norris.
Unfortunately, no option for “Who?”
Joffrey. Especially since she’s a stupid, skinny girl.
You left off the most important answer, the one right there in the source of your inspiration:
RIVER TAM BEATS UP EVERYONE!
Evil Clone River Tam!
I don’t even watch Burn Notice, but based on my Google results of trying to identify “Michael Westin and Fiona at once” that seems interesting. 
She wouldn’t need any fancy martial arts for that, though. The back of her hand would do nicely.
On the off chance people haven’t seen it, here’s my favorite fan-made video ever.
Though I would like to see her kill him with her brain.
I can’t believe geeks would actually be willing to see that movie. Its title font is obviously Papyrus. According to what the internets have told me, use of Papyrus as a title font is the entire reason that the movie Avatar was so horrible.
Came in here just to say this.
Well, now we are in my type of scenario – I like catfights a lot, and I love seeing sexy women getting KOed, as long as it doesn’t look realistic, with blood and bruises, etc. So I voted for Lara Croft, the Tomb Raider!
(I would also like to see River Tam KO my heroine, Panther Girl, or any of my sexy female characters, but they aren’t widely known, of course…)
Yeah, I had to Google the name, she is a character from Firefly.
Joss Whedon.
I love you, Joss, but legions of fans cry out for vengeance. You’ve broken our hearts too many times. And you killed Giles in Season 8 of the comics just because you felt like being a dick. So, unfortunately, River is going to have to kick your ass.
And you’re a better man for it 
(or lady)
(strikethrough added by me)
You forgot a few names on that list there.
I’d kinda like to see her square off against the “Cameron” terminator.
Most of the rest I can handle happening for dramatic purposes. But the one I listed was just mean, and Joss admits it.
This board really needs a “+1” button.