Most of the time those kinda scenes annoy me because it's so damn unbelievable. But I absolutely love the opening scene in The Matrix where Trinity kicks ass.

How about the last 20 minutes or so of Death Proof?

Kill Bill 1 and 2
Planet Terror

Serenity, when Summer Glau ("River") goes nuts in the bar.

That was one of the coolest ever.

Restaurant fight scene in Crouching Tiger, Hidden Dragon.

Get away from her, you bitch!

Jen Garner in The Kingdom. The girls from Descent on that final siege. The Biel in Blade Trinity.

Eowyn stabbing the Witch King in Return of the King.

Maggie Q kicking Bruce Willis' ass in Live Free or Die Hard was pretty cool.

Patricia Arquette whipping James Gandolfini in True Romance.

2LDK - the whole thing.

Kill Bill 2 - the Vernita / Beatrix opening rumble!! Great stuff.

Vernita fight was the first fight in KBv1, I thought the Elle / Beatrix scene was a lot cooler (from v2).

Tarantino makes a good female ass kicker .

I'll go with the chick from Survive Style 5 and Gogo's scene in Battle Royale.

Battle Royale Scene:
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The Survive Style 5 scenes are scattered throughout the movie, so that'd be a little tougher.

No...it would have been the coolest if Kurt Russells character had killed all the women within the first 5 seconds of them being on screen. This movie was one of the worst i have ever seen. All the way through it i just wanted all the women to die they were such unlikable characters. The acting was also just terrible. Is it Zoe Bell.....or whatever her name is...Uma Thurmans stunt double.....boy can she not act.

I agree...

Couldn't disagree more

When the girl finally gets her revenge in "I Spit on Your Grave", she pretty much kicks everyone's ass.

And for the record, The Bride in "Kill Bill" owns this thread.

I'll go on record with a vote for a scene from an upcoming movie, Harry Potter and the Deathly Hallows...

Princess Mononoke. San attacks Iron Town, fights her way through the guards, and has a catfight with the mayor

The bathtub scene. That is all.

Agreed on Kill Bill, The Descent, Aliens, and Death Proof. Some others not mentioned yet:

Sarah Connor attacks the Dyson residence (T2)

Ripley's nuke proposal: "They can bill ME!" (Aliens)

Ma Fratelli and the basketball of death (Deadly Friend)

Thelma and Louise turn the tables on the rapist.

Miho in Sin City.

"T2" Sarah Connor escaping from the mental hospital
"Aliens" Ripley (in body armour) vs Alien Queen

Too many to name, but for a few of my favorites:

Leeloo against the aliens in the hotel room,
Samantha Cain finally reverting back to Charlie Baltimore when she rises out of the water and caps Daedalus,
Princess Fiona against Robin Hood's guys in the forest in the first Shrek.

Milla Jovovich in RE3, fight scene in Vegas

Kill Bill was my first thought.