The Continentals' gender bending adventress Lady Fiona Fiziwigg. This men's suited, top hatted, two fisted, gun wielding, say and do as I damned well please agent in her majesty's service is more distressing damsel then damsel in distress as she investigates a series of brutal "mangling" murders uncovers a tangled web of intrigue, adventure and murder with her Continental Operative partner Jeffrey Tiffen Smythe in victorian England. Find it here.
About half of the cast of Cry Havoc, seeing as they're nearly all mercenaries it's not unexpected.
The Cyantian Chronicles: Silver and Celina best embody this trope. Quinn will, once she does more than spar with family and friends. Chatin, Cilke and a few others cover this trope to a (very slightly) lesser degree.
It helps that the majority of cyantians have some kind of combat training. Especially the members of the Akaelae family and the Mounty royal family. Which makes sense given the need to protect themselves.
Amy Fang, the Perky Goth heroine of Dead Metaphor has demonstrated Action Girl capabilities while fighting zombies hand-to-hand.
Nonami Mumei from Dr Nonami can frequently be found battling robots, mad scientists, and other villains.
Elf Blood, being an action webcomic with a majority female cast, would be positively weird without its share of Action Girls. Of note are two of the Incarnum characters: Shanna, a tomboyish brawler; and Carlita, an elegant superspy.
Virtually every female character in Errant Story qualifies, though special consideration goes to Sara, the resident warrior-monk. Time-mage warrior-monk.
Asuka of Everyday Abnormal introduces herself by killing six or seven Yakuza soldiers while barely breaking a sweat (although she nearly loses her eye). In her second appearance, she wins a fight with "The best hand-to-hand fighter on Earth" in a couple of seconds.
The title character of Evon: An Action Survivor when first introduced, she progresses from taking out the odd mook, to holding her own, solo, against a Terrible Trio of Cabal agents assembled to take her and Hero on.
Zeetha from Girl Genius is a warrior woman from a hidden, jungle city which might possibly have a matriarchal society (this is speculation). She appears to be a stronger warrior than any of the humans in the comic, although she is beaten in combat by the superhuman Baron Wulfenbach.
There's also that Baron Wulfenbach is perhaps the most badass individual on that planet. Really, losing to him is no shame for anyone.
That, and Word of God has confirmed he spent a few years amongst her people and is her father, though neither has realized that last bit.
The title character is a proficient in making and usingdeath rays and can hold her ground with a sword, but lacks the physique of a real action girl. Fortunately, Zeetha's working on fixing that.
In this comic, she defeats a half dozen guards singlehandedly with a weapon she's not even known to be proficient in, in a very short time span.
Miko might have been a stick-up-the-butt Knight Templar, but this is a woman that managed to solo the Order twice, defeated a minimum 15th level, artifact-enhanced cleric and can behead people with her feet.
Heck, don't forget Badass Normal / Mama Bear Kazumi. And those poor ninjas thought assassinating a woman who was six-months pregnant would be easy! Also Therkla seems to be one, though we see relatively little of her fighting skill.
Likewise, Lien (who's so badass that her paladin mount is a shark).
Pacificators are full of Action Girl, the most prominent being the main cast (five of 'em. Yes, you read that right) who are peacekeepers fighting to help bring the world out of the Second Dark Age.
Here's an example: In fact, the first time we meet them, MunecaPowell wiped the floor with two bodyguards who were much bigger than her.
Kira in Panthera not only is a star athlete at school, but also aced Panthera's battle obstacle course on the first try. Oh, she's a fire-powered tiger that fights against a secret government project with Panthera.
Kova, of The Player's Guide To S.I.S.U., is easily the toughest member of her team - the first time we meet her, she's duelling one of them, and takes him apart almost without suffering injury herself.
Freija certainly and too a lesser extent Rachel in The Senkari are action girls. Rachel is capable of putting aside her sword, Freija seems to want to be an Action Girl even when there is no Action to be had.
Captain Jordan Lee from Skins She holds her own against supernatural threats and she was the one chosen to lead the team of werewolves and vampires, despite being only human herself. The first time we friggin' see her, she has a werewolf on a leash. Now that's badass!
Scorpio, Taurus, Aquarius and Sagittarius on the hero side of Zodiac. On the villain side, the female ones are more crafty and seem to prefer to act behind the lines (such as Slaver and Legion), but Nightmare, Basilisk and Razor are straight examples.
Melody Meadows from RedSpaceBlues is a space mercenary with a gun though she fights better with he hands.