24: Jack Bauer especially but also many of his opponents. He'll use sneak attacks and break bones, kick in kneecaps, and shoot to incapacitate or coerce. His fighting style is brutal with little or no flourish. This gets taken to utterly pants-shitting levels at times. Early in Day 6 whilst tied to a chair and being tortured, he waits until the mook has his back turned, and removes the cuff on his EKG from his arm, causing it to flatline. He plays dead while the mook comes over to check on him and then takes a chomp out of his neck.
Andromeda: One of the Nietzschean's hats, Nietzschean crewmembers Tyr Anasazi and later Telemachus Rhade are usually the first ones to suggest retreating and/or selling out their allies when a situation appears hopeless. It might seem odd considering their Proud Warrior Race status but meshes quite well with their Social Darwinism, especially considering that their definition of "fittest" is "lives longest and sires the most children".
Had a few of these, which is surprising considering that it's high fantasy, and the protagonist is nearly indestructible. Especially when considering how over the top its parent show could be. Probably the best example would be Lindsey's hand. Lindsey dangles a scroll that Angel desperately needs to save Cordelia over an open fire while goading Angel. So Angel cuts the guy's hand off at the wrist then casually walks over and picks the scroll up.
And, lets not forget Russell Winters:
Lindsey: "So you kicked him out a window."
The Avengers: A producer's write-up on John Steed, to guide writers of episodes, specifically stated that "he fights like a cad and uses every dirty trick in the book..."
John Sheridan used a distress signal to lure a Minbari capital ship in an asteroid field mined with fusion bombs. Garibaldi put it best:
Garibaldi: "[...] Right now, according to his file, Sheridan is a good tactical thinker. He can take an inferior defensive force and turn it into an offensive force capable of taking on a better-equipped enemy. Now, he did it with the Black Star, he did it during the Mars riots. Now, you ask me, he is the one chance we've got to make it through this thing alive."
A double example with the Blackstar: the distress signal was genuine, the ship had been crippled by a Minbari ambush and left for dead, the Minbari were coming to kill a helpless opponent and he took advantage.
Batman: If you take out the wacky sound effect frames and just look at how Batman fights in the 60s TV show, you'll see that he gets fairly brutal. At one point, he rips a lead pipe off a wall and beats a mook with it.
Starbuck in the re-imagined show, particularly during the episode "Scar", wherein Viper pilots are confronted with a deadly, newly-motivated enemy sortie, who utilises all sorts of tricks and decoys.
Starbuck: 'This isn't dueling pistols at dawn, this is war. You never wanna fight fair. You wanna sneak up behind your enemy, and club 'em over the head. You see, Scar understands that. And so do I. So, that's why I'm gonna kill him.'
Of course, the most pragmatic thing Starbuck ends up doing in that fight is swallowing her pride and luring Scar into an ambush so that someone else can take the kill and get the glory.
Colonel Tigh took this trope to a much wider field during the occupation of New Caprica. Suicide bombers, random violence — "I'm on the side of the demons."
The best examples from this series comes from the defeat of the Judge and the final battle with Glory. The Judge was an immortal demon (meaning that you could cut him to pieces and he'd return alive as soon as the pieces are reassembled) and invulnerable to forged weapon: Buffy followed Xander's advice and shot him with a rocket launcher. Glory was a goddess too powerful for Buffy to match in normal combat: Buffy and the gang slugged her with the hammer of a troll god and a wrecking ball, and when Glory retreated and left control of the body to Ben Giles calmly walked up and strangled him, killing a goddess in the process.
Burn Notice: Michael Westen. As he explains in the Season 3 episode, "Friends and Family", "Spies are not trained to fight fair. Spies are trained to win." He always explains via voice-over what he's doing and why he's doing it. For example, in a car chase, he explains that small-caliber weapons can't penetrate the engine block, so it's best to aim for the windshield, or try to ricochet bullets up from the ground, as it's really hard to drive when you've got bullets coming at you from under your car.
He once used a copy of Cat Fancy magazine to beat up some loan shark thugs. In the first episode, he teaches self-protection techniques to a kid with a bully problem, including feigning submission and headbutting
The other two members of Michael's Power Trio, Sam and Fiona, fit this as well. One episode has Fiona showing that she had no qualms about subduing a thug she was trying to capture with a well-placed beanbag shotgun round to the thug's groin.
Camelot: Gawain explains the philosophy of pragmatic combat to Arthur and his merry men. It takes them a while to accept the idea.
Community: Pierce in the episode Comparative Religion claims to be using this to try and help teach Jeff fighting, but actually he just wanted an excuse to kick Jeff (and Troy) in the shin.
Deadliest Warrior: Frequently argued about by supporters of warriors who prefer ambush or avoidance tactics rather than the toe-to-toe duels that the show always assumes.
Doctor Who: the Doctor usually shys away from guns. Not so for the Sixth Doctor, who upon faced with an army of Cybermen simply picks up a blaster and dispatches the lot.
Firefly: Most fights include dirty tactics, such has hitting people from behind, throwing sand in their eyes, hitting genitals, surprise attacks, etc.
Captain Malcolm Reynolds, especially, seeing that he has no problem hitting people from behind, turning a duel with swords into a fistfight, and even throwing people into jet turbines or, worse yet, space.
"Gameof Thrones": When Bronn wins his fight as Tyrion Lannister's champion by somewhat unconventional means, Lysa Arryn reproaches him: "You do not fight with honor." Bronn indicates his slain adversary and answers: "No. He did."
Hawaii Five-0: Somewhat Played for Laughs in the episode "Kekoa". Steve tells the Killer of the Week, a trained martial artist, to pick on someone his own size. The killer charges and Steve draws his gun and kneecaps him with an almost bored look on his face.
Highlander: The Series: Methos. If the fight's going against him, Methos is not above feigning helplessness (such as pretending to slip) and then, when his opponent moves in for the kill, drawing a hidden dagger and stabbing him.
Methos is the oldest Immortal. He's so old that he doesn't remember how old he is. He remembers the first civilization, and he was already old then. There's only one way to become the oldest Immortal: Be very good to your friends, have no mercy for your enemies, and always, always, know which is which. This was explicitly referenced a few times; many of his friends hail from eras of formal combat and take Honor Before Reasonvery seriously, but he was ancient before honor was even invented.
I Carly: Sam will cheat as much as possible in any combat related event. She ran around with an extra half-dozen blowtubes for her game of paintball assassin with Spencer. Apparently she's also knocked out a trucker with a jug of milk, according to Carly.
Kamen Rider Dragon Knight: Grant Stanley- AKA Kamen Rider Camo- is an underground martial artist who is not above attaching wrenches to his fists to win a fight. Karma hits him hard when he is vented (killed, but not really) by Kamen Rider Torque and his massive arsenal of guns.
Kamen Rider Torque is the only Rider with an arsenal of guns; he never fights without using them and it is rarely a fair fight. He is only defeated by Kamen Rider Strike- whose vicious and close-range fighting style and powerful contract beast (and pension for dodging bullets) rendered Torque's guns useless. It is demonstrated quite clearly that Torque cannot fight at all without his weapons.
Many of the Riders have tactics and weapons that could be considered dirty, even the heroes: Siren can transform into a storm of feathers and Wing Knight can spawn clones of himself.
Law & Order: Special Victims Unit: In the Season 10 episode, "Crush", Stabler attempts to question an arrogant suspect in a gym in a boxing ring, only for the guy to tell Stabler to wait until he's done. Stabler gets into the ring, and the guy to takes a swing at him. Stabler dodges it and knocks him down, to which the suspect yells that it was a cheap shot, to which Stabler replies, "I though it was a street fight".
Legend of the Seeker: In one episode, Kahlan is kidnapped and kept in a dungeon. She finally escapes after the guards give her a plate of stale bread to eat. She takes the metal plate, folds it in half, creating a sharp corner, and stabs her guards with it. Stay in the Kitchen does not work on this woman.
Reese: So, once you've taken out his eyes, you can take your time and really get creative. Personally, I like to leave at least one sense working, so he can tell what's happening to him.
Married... with Children: In one pirate-themed episode, Captain Courage (Al) and Rubio the Cruel (Steve) are sword fighting for Scarlett's (Peg) freedom, Rubio boasts, "How can you think to beat me? I was taught swordfighting by the finest teachers of the finest schools in Europe!" Courage simply says: "Oh yeah, I learned in the streets!" and knees Rubio in the nads, winning the battle. Bud also applies this trope on a few occasions. When he gets into his first barfight at the nudie bar, a seasoned veteran decides to give the "rookie" a free shot. Bud immediately smashes him over the head with a chair, which makes Al very proud.
Merlin: Merlin is enough of a Magic Knight to give lower enemies a fair fight with a sword...but why would he do that when he could just use his magic to hit you with your own weapon, trip you up, drop tree branches on you, or disarm you and let his Master Swordsman best friend King Arthur clobber you? He even cheats for Arthur in a few occasions, breaking the saddle girth on mounted knights and disarming Arthur's opponents even if it looks like Arthur could handle them, just in case.
Murdoch Mysteries: Julia Ogden is a prime example of a Combat Pragmatist. She will attack you from behind or use her skill with scapels to mortally injure her if you attack her or someone she cares about.
The Office (US): The duel between Michael and Dwight proves the point. While Dwight uses honorable combat and martial arts, he gets easily defeated by Michael's schoolyard bully tactics. Plus there was that other duel Dwight fought against Andy. Dwight again tried to fight honorably, but Andy opted to use his electric (and therefore silent) car to sneak up on Dwight and pin him against a fence.
While in professional wrestling cheating to win a match usually makes you a bad guy, several noted wrestlers have gotten famous as nontraditional babyfaces who beat the heels through all manner of dirty tricks. The two most famous examples would probably be Eddie Guerrero, who would win matches by (among other things) throwing a chair to an opponent and flopping to the mat as though he had been hit and was one of the most beloved men in the industry despite having "I lie, I cheat, I steal" as his personal slogan, and the legendary Ric Flair, world renowned as "The Dirtiest Player in the Game" who would beat the opposition with eye gouges and the dreaded "testicular claw".
You can call this a gutless rationalization if you like, but technically Eddie's chair trick wasn't illegal because it didn't require him to touch his opponent. The only three actions that can get a wrestler disqualified are 1) hitting your opponent in the groin or using another dirty strike, or using a dirty grapple and not releasing it in five seconds; 2) hitting the referee; or 3) hitting someone not involved in the match, in which case you essentially get disqualified for being a dick. You can also get disqualified if another person hits your opponent or the referee, which may or may not be fair (depending on whether the other person is your friend delivering an epic beatdown, or your enemy hitting someone just hard enough to stick you with a DQ).
Finlay, in his current WWE run, is a more recent example. To Finlay, every part of the ring is a weapon, including the apron (which he utilizes as a net to trap wrestlers trying daring-leap-to-the-outside or baseball-slide maneuvers). And, just in case things start really going south and he needs a real weapon, he always has his shillelagh waiting for him in the corner. And did we mention he's a Face?
And then there's Money in the Bank, a Gimmick Match whose winner can claim a title shot any time within the next year. It usually gets cashed in right after the current champ has gotten thoroughly beat up by someone else.
Revolution: Miles prefers to just kill his enemies, so they don't bother him later. "Chained Heat" has him sparing the bounty hunter Jacob at Charlie's urging, but when Jacob sells them out to the Monroe militia, Miles makes sure to kill him off the second time they meet. "Nobody's Fault But Mine" has Rachel lulling the psychopath rapist Will Strausser into a false sense of security before stabbing him the heart.
The Rockford Files: Jim Rockford definitely fits. Whether it's low blows, improvised weapons, or distractions, he uses any dirty fighting technique he can think of. Lampshaded in one case, where he makes sure he has the Mook's attention, goes into the bathroom, spreads soap all over the floor, slips a roll of quarters into his hand to up the impact on his punch, and, when the guy follows him in, goads him into attacking first so he'll slip and be easier to cold-cock. He then tells the recumbent idiot that "the problem with Karate is it's based on the ludicrous notion that the other guy is gonna fight fair."
The Sarah Connor Chronicles: Cameron does not know of any other way to fight. For example, at one point she casually shoves another Terminator through a wall and blows its prone body apart with a grenade launcher. She also has no qualms with dropping a Terminator down an elevator shaft, and then dropping the elevator on said Terminator. Being a Terminator herself and given the kind of opponents she faces, this pretty much comes with the territory.
Seinfeld: One episode has Jerry and George ask Elaine which of the two would win in a fight. Elaine says George, on the basis that he would fight dirty. George happily admits it, and Jerry happily accepts it. This is confirmed in a later episode where the three of them fight, and George does win.
Smallville: Clark Kent of all people does not believe in a fair fight. His usual strategy boils down to "clock you in the head from behind at 500 miles an hour." Tess Mercer is just as bad, if not worse.
Stargate Atlantis: In one early episode, Teyla hands Sheppard's ass to him in a sparring match with melee weapons, and Teyla remarks that if it were a real fight, he'd be dead by now. Sheppard replies that if it were a real fight, he would have shot her by now. You don't bring a couple of sticks to a gun fight.
Weyoun. Of the more strategic type than actual throw-downs, the idea that there are 'rules' in combat is a notion he is only aware of so that he can manipulate other people. This may be a trait of the Vorta in general, given that they are a genetically engineered race.
And Major Kira. As has been noted elsewhere, fair tactics do not keep one alive in the Bajoran Rebellion. Therefore, Kira doesn't use them.
By Klingon standards General Martok can seem like this. He is perfectly willing to perform hit and run, and strike weak enemies, and cut-off supply lines rather than directly engage. Being a Klingon, he really doesn't like these tactics (They're not very fun), but he feels that winning the war is more important than earning honor and glory in individual battles.