Mazinger Z: The titular mecha not only sported a Rocket Punch -it is the Trope Namer and Trope Maker, in fact-, but in one episode extendable cutters were added to the forearms (the Iron Cutter). And in another episode, its fists got reinforced to make them sturdier.
In the FORCE manga. Veyron's "Claw Grab" seems to fit this trope as it's a claw-shaped gauntlet that allows him to fire non-magical explosive attacks with internal fluids and also seems to enhace his already impressive strenght as one of it's first demonstrations was blocking and damaging Subaru's own powered gauntlet mentioned above. As it's name implies, it's really good for grabbing things and make them explode ...like limbs ...or heads.
Allen Walker from D.Gray-Man, and his left arm. Normally, it's an unsightly Red Right Hand, though he's one of the nicest guys, ever. When activated, it becomes a monstrously huge metallic paw with large, wicked claws. There is actually a scene where he points out that his claws are too big for him to make a fist. From the same series, there's also Lenalee Lee, whose special weapons are the Dark Boots, which allow her such awesome speed and mobility she might as well be flying, and deliver brutally hard kicking attacks.
As his left arm evolves, though, it becomes able to turn into a BFG and a Beam Saber before becoming a smaller, sleeker claw with a prehensile cape, and finally a BFS.
Busou Renkin; Kinjo, one of the humanoid homunculi mid-way through had an Alchemical Weapon Gauntlet, the Peaky Gulliver, and was capable of making that fist freakishly large and crushing anything under its weight.
Hell Teacher Nube's hand, in which a supreme Oni is sealed, is overwhelmingly powerful on its own for ordinary (or not so ordinary) fisticuffs... but later on, Nube learns to release just enough of the Oni's power to turn it intobladed weapons, shields, gigantic "nets" made of blades and spikes and bone, or even let it take over the rest of his body to overcome particularly nasty foes.
Macross Frontier notably uses this a few times, once as a homage to the original Macross, and in the Grand Finaleobliterating a multi-kilometer mecha with the Power Fist of another multi-kilometer mecha.
By Macross Plus, the aforementioned energy shields have been miniaturized to the point where standard Valkyries have them, and a few pilots in this series and Macross 7 use them to perform a "Pinpoint Barrier Punch".
Tanarot from Macademi Wasshoi has a pair of oversized boxing gloves that serve as her primary weapon. This is a perfect match for her personality, which is a ball of energy bound to blow up things. She's very good with them.
A variant is found in Bubblegum Crisis: Knuckle Bombers, which are shaped charges attached to a guard over the fist of the heroines' Powered Armor. Understandably, getting punched by this hurts.
Katekyo Hitman Reborn!: The X-Gloves worn by Sawada Tsunayoshi (and their predecessor, the I-Gloves worn by Vongola I.) Not only do they light on fire, but they allow flight, absorption of other flames, and the ability to FREEZE.
In Blaster Knuckle, main character Victor Freeman's weapon of choice are his titular knuckles. It's a gauntlet with four bullet chambers over each knuckle that shoot silver bullets when he punches monsters. The result is a wonderfully gory explosion.
One of the weapons used by the operatives of Section Nine in the Ghost in the Shell anime can essentially be summed up as tazer knuckles. They're primarily for use against combat-rated cyborgs.
Occult Academy's: Generally played for laughs, but when Maya gets angry at the male lead, her response will sometimes be to take the bracelet she wears on her right wrist, slip it over her fingers, and use it as an impromptu brass knuckle.
Berserk: It's not often touched upon, but Guts has used his mechanical hand as a weapon in itself against several of his more human enemies.
Fullmetal Alchemist: Major Alex Armstrong has his transmutation circles on giant brass knuckles.
One Piece introduces Gedatsu with a variation of this trope. He basically puts rockets on his elbows to make his punches faster and therefore stronger.
A Silver Age story had Batman gain this power temporarily as a result of an experimental chemical splashing on Bruce Wayne's hands, which was later activated when Batman got splashed by a fire hose from a criminal (this isn't Super Strength; his hands were just reinforced to withstand impact). This example overlaps with Blessed with Suck as Batman realized this meant he can't fight someone directly, as punches that could dent wrecking balls or smash through brick walls would kill people out right.
The Fantastic Four enemy the Super-Skrull likes to turn his hands into copies of The Thing's (no, not that one) and combine rocky-skinned superstrong punches with the long reach of Mister Fantastic and sometimes adds a flame and forcefield combo to add to his punches', er, punch. In fact he once used this destructive combo-punch and his Voluntary Shapeshifting powers to impersonate Powe...I mean, Iron Fist.
The Jager Maxim of Girl Genius wears one of these into combat. Similar devices have also been seen being worn (in flashback) by Dr. Mongfish and The Other.
Chase of Runaways wore the Fistigons, "the most powerful gauntlets ever invented" for a while. And he has recently retrieved them thanks to the wonders of Time Travel.
Both versions of Goldengloves from Astro City use super-powered alien boxing gloves as their main gimmick.
The Satan Claw worn by Baron von Strucker, the original Supreme Hydra in the Marvel Universe. Unfortunately for him, the first person he used the metal weapon on was Magneto.
Later, The Punisher acquires one of the Satan Claws and proceeds to beat the snot out of Rhino with it.
Southpaw (from She-Hulk), Gauntlet and Armory (from The Initiative), all created by Dan Slott, and all posessing alien gloves that project energy fists, but can't be removed. All three weapons are related (Southpaw and Gauntlet's were worn by the same alien; Armory's belonged to the one he was fighting.)
Strontium Dog protagonist Johnny Alpha used Electro-Knux when engaging in hand to hand combat. Having been created by the same writer, the technology has also appeared in Judge Dredd.
Iron Fist's superpower is the ability to concentrate his chi in any part of his body, most commonly his fist, and render it "like unto a thing of iron." The better to punch you with, my dear. His charged-up fist also glows and shows the Kirby krackle, because.... hey, why not?
Hawkman wore a Magitek glove called The Claw of Horus that drew power from the magnetic core of the Earth and knocked The Man of Steel out with one punch. The glove was later a plot point in Brightest Day.
The Dark Knight has Batman's hydraulic gauntlet, which can bend gun barrels and pierce the bodywork of a van.
Gamera in the film Gamera 3 Awakening Of Irys gains the ability to form a fist out of plasma after his real hand is amputated. He uses said plasma-fist to Punch a hole into Irys and kill him.
Turkish Star Wars: Prior to the final battle, the protagonist melts down his golden BFS and turns it into a pair of magic golden gloves.
Near the end of Transformers: Dark Of The Moon, Optimus Prime deploys a claw attachment to his punching hand, allowing him to basically tear an enemy in half. Of course, since Optimus is 40 feet tall and made entirely of metal, his hands fit this trope all the time.
In a obscure John Saxon movie, The Glove, prominently features a so-called "riot glove", armored with metal plates and allegedly used by police to beat up hippie demonstrators.
Pacific Rim: Cherno Alpha, the Russian Jaeger, has disproportionately large fists when compared to the rest of its body. Said fists have hydraulics to add some power to the punches and Tesla coils that shock Kaiju on impact.
In The Malloreon, Zakath uses a cestus (essentially a boxing glove that's weighted and spiked to hurt more instead of less) in his first fight after joining the group because he's out of practice with his sword.
In Animorphs, Marco uses his gorilla morph's fist. "Gorilla. The outward expression of my inward rage". There are also many remarks in other books about his 'canned ham' sized fists.
Also many instances of Rachel's bear paws coming into play in this manner.
Live Action TV
Doctor Who: In "The End of Time", Rassilon wears a medieval-style gauntlet on his left hand that can act as a remote control for other devices and can vaporize a Time Lord with a gesture (sorry, no regenerating!). It wasn't used much, so we don't know what it's really capable of.
William Regal, for a while, had a gimmick where he would win his matches thanks to "The Power of the Punch". Unbeknownst to the Easily-Distracted Referee, said punch was powered by a set of brass knuckles secreted in his trunks.
The Trope Namer is Warhammer 40,000, where our Crimson Fists friend in the picture above comes from, which features among its close combat weapons, massive mechanical fists a good three to five times regular size that are loaded with servo-motors that radically increase the user's strength and wreathed in an energy field that tears apart anything it touches on the atomic level. The game also features:
Power claws, which are the same thing but with giant crushing blades instead of fingers;
Lightning claws, which are four or five giant blades in the place of the fingers (or on some other units, Wolverine Claws on the back of the hand) wreathed in an armour-ignoring energy field in the same way as power fists;
The Scorpion's Claw, a powered scorpion claw with a built in gun that fires thousands of molecule-thick ninja stars;
The chainfist, a power fist with a giant chainsaw also wreathed in the aforementioned destructive energies bolted to the knuckles, which is canonically capable of tearing through metres of nigh-indestructible adamantium with no problems. It is, however, so heavy it can only be used by suits of power armour so tough they can survive being trampled by hundred-metre-tall Humongous Mecha.
The Unique Power Fists used by some of the independent characters, like Huron Blackhart's "Tyrant's Claw", which has a heavy flamer built into the palm, or "the Talon of Horus", Abaddon's lightning claw with a Twin-Linked Bolter.
Titan close combat weapons are often enormous Power Fists. One type is the Corvus Assault Pod, which is a combination of a powerfist and huge drill with room to house a boarding party inside. It's used to punch a hole into the enemy titan or building and release the boarding party to kill anybody who survived being punched by a Humongous Mecha.
Commissar Sebastian Yarrick lost an arm up to the elbow to an Ork Warboss. Yarrick, being the Bad Ass that he is, would not stand for this and immediately decapitated the Ork, and now uses the Ork's power klaw in place of his severed limb.
And then there's Tyberos, The Red Wake◊, who combines power fist, chainfist, AND lightning claw into two giant shredding devices named Hunger and Slake. Run away.
Now even the Tau have their own version: the Onager Gauntlet. Created during the Damocles Gulf Crusade, the Gauntlet was meant to allow battlesuits to take on heavy Imperial armor when ammo was running low.
Warhammer has the ogre ironfist (a sort of hybrid shield and punch dagger) and Dwarf engineer Burlok Damminson's Steam Punk claw.
"Gauntlets of Ogre Power" are a classic Dungeons & Dragons item, though the manual strength enhancement isn't limited to bare hands.
Among the "components" available to warforged in Eberron is the battlefist, a +1 weapon which looks like a massively oversized spiked gauntlet and increases the damage of the warforged's natural slam attacks.
A prestige class introduced in Magic of Eberron, the Renegade Mastermaker, is basically a magitek cyborg, capable of replacing one hand with a metal one for a slam attack of his own.
And it's survived into the 4th edition; now an artificer paragon path called the "Self-Forged." It begins with replacing one hand/forearm with a "Battlefist," a magitek prosthetic that counts as a mace-class weapon in combat and which is used for the path's attack powers... the second of which is effectively a Rocket Punch!
Rifts has its own claw-based variation, usually of Wolverine-esque vibroblade claws mounted on the vambrace of a suit of armor or Powered Armor, and normally three in number.
The RPG SLA Industries has several examples of this trope. The three main ones are the GASH Fist (a powered fist with a large blade attached, much like a katar), the ITB Mutilator (a powered fist that, for unspecified reasons, causes more damage due to vibrational actions) and the JOLT fist, which deals no damage but acts like a finger tip-mounted taser instead.
Exalted has smashfists, an artifact weapon that is pretty much Exactly What It Says on the Tin. In addition, Lunars can incorporate special tattoo artifacts into the full-body moonsilver tattoos that every Lunar in the Silver Pact possesses; at the expense of having to permanently attune to the artifacts in question, they can't be stolen and are always available to the Lunar, even when shapeshifted. Smashfists are among the artifacts compatible with this method, making it possible to have a literalPower Fist.
Then there's Alchemicals, who can install a "Transcendent Multimodal Artifact Matrix" to transform their hands into smashfists (or just use regular ones - artifacts are nice and cheap when you live in the heaviest magitech environment known to man), and a Piston-Driven Megaton Hammer in their wrists to produce a lot of damage.
The latest art for Kird Ape has powerfists made of rock.
GURPS has brass knuckles, which only slightly increase damage but also allow you to attack targets that would otherwise damage your hands. GURPS: Martial Arts has the Bagh-Nakh, bladed hand, cestus, myrmex and sap glove. Ultra-Tech has and advanced version of brass knuckles and zap glove, along with a system that makes your punches stick grenades to the enemy.
High-Tech has the Pistol Glove, which shoots a bullet when you land a punch.
7th Sea: there are two preeminent fighting styles in Eisen. One involves a Zweihander and your face. The other involves a regular broadsword, a Panzerhand (lit. Armored Fist, a heavy plate glove, possibly made of the local Adamantium), and your face. It may not be as graceful as Montaigne fencing or as subtle as Vodacci dagger-fu, but by God it's efficient. There's also a lesser known fighting style where a panzerhand is worn on both hands at once. Its primary move is just yanking the weapon out of a person's hands and then beating them silly.
Battlemachines' power fists are mounted onto giant giant mecha and can throw anything they kill around. You can also upgrade one to set stuff on fire, or explode.
The Retribution of Scyrah faction in Warmachine can field Battle Mages, who are equipped with magically-enhanced gauntlets to punch the enemies of their people into next week.
Xenosaga featured Ziggaurat 8 ("Ziggy"), a cyborg whose left arm and both legs are visibly robotic and used to devastating effect. Shion used an odd sort of power-knuckle device equipped with various gadgets and weapons.
Yang Fang Leiden only uses claws to add elemental properties or debuffs to his attacks. Then again, this is a man who used his body to make the Tower of Babil's cannon misfire, so what's a weapon gonna do for him?
Rikku's in FFX. All of her weapons are fists, including her best, the God Hand. And many, like any other weapon in the game, had extra properties, ranging from status effects, to element affiliations, to the vaunted No MP ability.
In the games where monks/martial artists appear in Dragon Quest games, there is at least a few weapons of this type (although most monk and martial artist weapons are of the claw variety).
Nero's Devil Bringer from Devil May Cry 4. Dante has the Ifrit in the first game and Beowulf in the third, and the Gilgamesh in the fourth. The later two are gauntlet-and-shoes comboes, while the first are just gauntlets.
The Glutton of Bloodline Champions wear wooden spikes on their right hand, with other alternate weapons for them being even fancier weapons to cover their hand. Except for the one which is basically a hollowed-out log on their hand.
Fallout had the "Big Frigger" Power Fist. Fallout 2 adds the Mega Power Fist which was the same except, you know, fistier. Fallout 3 returns to the original Power Fist, but also includes the Deathclaw Gauntlet, which consists of strapping the hand of the titular wasteland beastie to the end of one's arm. This doesn't sound much until you try it and realize that it ignores the target's armor.
Fallout Tactics adds the Impact Gloves ("Pneumatic Power Fist" in Fallout 3) and Punch Gun, a leather and metal gauntlet that would fire a shotgun shell point blank on impact.
Also, in Fallout 3, one can't forget the unique weapons The Shocker (an electrical power fist) and Fisto! (exclamation mark included).
It's possible to learn to craft dog tags into a set of Wolverine Claws, essentially holding sharpened tags between one's fingers. There's a unique version appropriately named Recompense Of The Fallen.
And lastly, there's plain jane knuckle dusters, in both the brass and the spiked varieties.
Old World Blues adds the steriliser glove and corrosive glove: rubber safety gloves covered in chemicals that set enemies on fire and drain health over time, respectively. There's also the Saturnite Fist, which is a slightly more powerful version of the normal Power Fist, but taking it to your world-destroying toaster (yes) will give you the option to superheat it, which makes it stronger and lights targets on fire.
Oh, and you can't forget how some of the Ghost People in dead Money have a weapon that is literally a bear trap strapped to their fist.
And in Lonesome Road comes the Industrial Hand, which adds a rather gruesom buzzsaw blade where the weapons punches so you can slice and dice as you ground and pound.
One last piece of DLC goodness ... the Two-Step Goodbye. Power fist, check. Shotgun, check. Critical kills cause a grenade-like explosion? Ka-boom.
Robo of Chrono Trigger fights with his fists, which he can replace with better fists through the game, so he mostly counts. He's also got a kind of rocket punch. Cavewoman Ayla fights completely barehanded, and so falls under a different trope.
Sonic the Hedgehog: Knuckles the Echidna has the Shovel Claws in Sonic Adventure and Sonic Adventure 2. In the former game, he also gets the Fighting Gloves. They're yellow.
Darksiders features the Tremor Gauntlet, a huge lighting-wreathed glove granting War a powerful area-effect attack. It bears a striking resemblance to the Power Fists of Warhammer 40,000.
World of Warcraft has Fist weapons, often of the claw variety. Back at the game's advent, they were generally overlooked and not too common to begin with. Starting with the first expansion, however, Blizzard recognized the potential greatness of this trope and fist weapons became vastly more common; there is usually a fist weapon in every freshly released raid dungeon, and it is often looking awesome and is a great choice for any melee specialization that uses the Agility stat - namely Combat (non-dagger-user) Rogue, Windwalker Monk and Enhancement Shaman.
Several of Mega Man's weapons are Power Fists, such as the Hard Knuckle in Mega Man 3, the Mega Arm in the Gameboy V, and the Super Adapter in Mega Man 7.
Zero's "Z-knuckle" (a chip embedded in both hands) expands his Mega Manning ability; it allows him to steal weapons from normal Mooks so he can use them for himself. And, according to official art, his Evil Twin Omega Zero also has one, and is supposedly the basis for the Giga Attacks in the X series (appropriate, since Zero in his original body AKA Omega always performs his Giga Attacks by punching the ground).
Spark Mandrill gains this ability in the remake of the original Mega Man X.
After Duo crash-landed in Mega Man 8, he was so badly damaged that Dr. Light had to completely rebuild his body. The only features left from his original body were the jets on his back and the Duo Knuckle on his left arm.
Regal from Tales of Symphonia fights with various greaves around his shins for kicking, leaving his hands purely for balance as he's sworn never to use them for killing. Not that his hands could be used since they are shackled, which he prefers. (He gets rid of them in the sequel, apparently.)
A better example would be Yuri Lowell from Tales of Vesperia, as he can use an assortment of power gloves and spiked knuckles as a secondary weapon.
Akihiko Sanada from Persona 3 fights with an assortment of fist weapons.
His standard being a pair of blue boxing gloves.
Drachma from Skies of Arcadia fights with various attachments to his mechanical arm. As appropriate for the Sorting Algorithm of Weapon Effectiveness, you find various outlandish attachments of all kinds (such as a hook, an ancient magitek grappling claw and a drill), all of which are perfectly compatible with his arm, all over the place. Apparently there are a lot of other people running around with robot arms; you just never meet 'em.
Fist weapons are a main class of weaponry in the Disgaea series. While they all look alike, their description varies between realistic knuckle-type weapons, monstrous appendages, martial-arts techniques, and comic relief (including the Megaton Punch, "Guaranteed to turn your enemies into A Twinkle in the Sky!"). The magichange weapons are more distinctive, being visible during attacks, and generally looking like the hand or head of the monster that created it.
Taken to extremes in Disgaea 4, where magichanging a giant monster gives you a power fist that's almost as big as the wielder, on top of allowing you to wield two of them at the same time.
Potemkin of Guilty Gear actually both uses and somewhat subverts this. Mounted on his fists are extremely heavy gauntlets with built-in shotguns - but his instant kill attack actually involves him stripping off all the heavy metal gear he's wearing, which are actually inhibitors to prevent him from misusing his physical strength. He then punches his opponent. Once.
Phantasy Star Online and its sequel have fist weapons, which range from simple gloves to massive gauntlets several times larger then your character's actual hands.
Several chips in the Mega Man Battle Network games are built around giving Mega Man a huge fist, often with special abilities. The Guts Punch and Bronze/Silver/Gold Fist series chips all have arrow commands you can do to make their attack or range expand, and the Cold Punch chip...well, just freezes things. In the anime, Heat Guts style also gives Mega Man a huge fist and a rock-hard punch. Later in both game and anime, Rock can take on the attributes of the series' native punching expert Gutsman, and his default weapon becomes the Guts Punch.
Savyna's weapons in Baten Kaitos are all some variation of brass knuckles or fist blades. Ayme also uses certain tonfa-like weapons in this manner.
Gracia from Samurai Warriors 2: Xtreme Legends fights with her bare hands while wearing special bracelets. Unusually for this trope, her attacks are incredibly weak, much moreso than the other characters who use some sort of weapon. She compensates by having one of the best musou attacks in the game, and exceptionally powerful and useful musou-meter-powered special moves.
In Team Fortress 2, the Heavy recently received a pair of unlockable boxing gloves: the Killing Gloves of Boxing. They're actually a bit of a variation, in that the gloves don't directly increase his melee attack power; rather, after killing someone with the KGB, the Heavy gets 5 seconds of 100% critical hit chance, which apply to any of his weapons... But if he just keeps using the gloves, the timer tacks on another five seconds with each kill, allowing him to rack up a chain of deadly fistings. He's since gained access to the Gloves of Running Urgently (which make him much faster but drain his health) and the Fists of Steel, an actual pair of metal gauntlets.
The Engineer update yielded The Gunslinger, a mechanical glove that boosts the Engie's health and makes mini-sentries. On top of that, every third punch with the mechanical hand that connects has a 100% chance of a critical hit.
Stone Melee Heroes and Villains in City of Heroes and City of Villains can make their own granite fists for some of the earlier attacks. There's also the Energy Melee set, which focuses on this.
The Counter Sword in S4 League keeps a small sword in the right hand, but it's only used for the weapon's weaker attacks. Counterattacks and the weapon's uberpowerful Jump Attacks and Strong Attacks instead use a massive armored gauntlet, nearly as large as the player character.
In the older Bionic Commando games, the bionic arm acted as a sort of secondary weapon, allowing you to block shots and push enemies around. The recent remake allows you to use it to more directly kill stuff.
One pilot's machine is tailored to deal damage using power fists. Or rather, the "Jet Magnum", a normal, giant robot fist, with plasma charged stakes that explode upon contact with the enemy, who usually then explode.
Master Monks in Shining Force II equips fist weapons to counter their abysmal base Attack power, due to being healers previously before promoting. They still manage to turn the class into a walking death machine though, due to the fists having the highest attack ratings of all the game's weapons.
Prototype: One of the powers of Alex Mercer is turning his fists into huge bashing clubs.
Area from Street Fighter EX 2 and EX 3 fights with a miniature rocket launcher attached to her right arm.
Ratchet & Clank has a metal boxing glove called the Walloper, as well as other gloves that dispense weapons such as bombs and automatic turrets.
In Assassin's Creed II you can buy a Metal Cestus for Ezio. Oddly enough, it's only for one hand.
Being Warhammer 40k, Dawn of War features Power Fists as melee weapon upgrades for Space Marine and Chaos Marine officers, switching out the barely weaker Power Swords. They ignore armor which means a nasty surprise to anyone who decides to charge the squad (since Assault Marines and Chaos Raptors are better at close combat than their regular counterparts).
Ork Warbosses and Nobz can also be upgraded with Power Klaws which perform the same function.
The Adventures of Dr. McNinja featured a person who invented rocket boots. He used them to kick people, a rare example of a kicker for this trope and a practical use for otherwise silly technology. He was killed one night by assassins because he didn't wear his rocket boots to bed
At Whateley Academy Chaka gets a set of power gauntlets as a christmas present. They only work twice a day and require her to call her attack but they will go through the local power armour with little difficulty.
There's also "Dark Claw," the leader of a gang of thugs working for Lady Jettatura who was given a massive magical gauntlet to make him more useful.
Stinkoman 20X6: Stinkoman kills a giant robot in one level of his game, and then attaches the robot's fist to his own arm for no apparent reason. It's the size of his entire body, and he doesn't even punch anyone with it, he uses it as a giant shield.
Kim Possible: When Shego isn't using her glowing energy as a ranged attack, she uses it to power up her punches in combat. The energy exerts concussive force on her target, and she can even use it to burn things to ashes.
Gemini has a prosthetic hand that can deliver electrical shocks and launch miniature missiles.
He-Man and the Masters of the Universe (1983): This is Fisto's power. Makes sense. In one episode of the remake, he successfully uses it to distract an enemy so that he can punch him with his other hand. It's not quite clear how that works.
Fisto: See this hand?
(Mook glares at giant hand, Fisto punches him with his normal hand)
Fisto: Should've paid attention to the other hand.
It's pretty clear how it works. Fisto did just punch the guy, after all. It doesn't seem so much a distraction as much as plain trolling.
Lugnut of Transformers Animated can perform what fans have referred to as "the Punch of Kill Everything." His fist produces a bomb, and when he punches the ground with it (which he sometimes does with a jet engine), it sends a devastating shockwave (no, not that Shockwave) in all directions (somehow not damaging him). Of course, it can also be an Achilles' Heel: hit his fist before it hits the ground, it goes off early and he takes the brunt.
Transformers Cybertron joins this with Combining Mecha to give us Savage Claw Mode. Leobreaker transforms into a massive arm that can take the place of one of Optimus Prime's arms (Optimus must be in Super Mode, though). It becomes even more devastating when Leobreaker deploys his CyberKey-activated claws, which extend over the fist. With the claws out, Optimus can perform an attack inspired by Goldymarg's Shining Finger move. After Megatron creates Nemesis Breaker, an Evil Knockoff of Leobreaker, he can combine with N.B. for Dark Claw Mode.
Used a few times in Avatar: The Last Airbender , mostly by earthbenders to surround their hands with stone (or in Toph's case, metal via metalbending. The Dai Li agents late in the second season use special stone gloves that they can detach and launch at opponents.
In The Legend of Korra, the Equalists use electrocution gloves to dispatch their enemies, which Asami Sato uses against them.
Junko from Storm Hawks has his "Knuckle Busters", which enhance his strength and punching power when activated, though he doesn't really need them.
Xiaolin Showdown: The Shen Gong Wu Fist of Tebigong grants the user this ability.
The stun glove, a glove that shocks anything it touches when turned on.
The other obvious real life example would be brass knuckles/knuckle dusters/etc., which are illegal in much of the United States. Slightly more legal are SAP gloves, which are partially filled with lead shot or powdered metals to add more "oomph" to a punch while reducing the chances of injuring one's hand when hitting someone. They see some use among law enforcement officials.
The tarch, a combination of a metal glove, a sword, and a shield, all rolled into one. Used by 16th-century Russian soldiers when defending against a siege. Not very useful in open combat. See here◊ for an image.
General Electric's "Hardiman" system has particularly terrifying hydraulic claws (as may be seen here). They'd need the whole exoskeleton to be worn to use in a standalone fashion, and GE never solvedpotentially lethal positive feedback loops in the control system. Man amplifiers are coming back into fashion though...
For kids, there's also the B.I.G. Power Hand, a toy composed of a giant mechanical hand with a small glove rigged so that each finger is independently movable by the wearer.
The modern boxing glove is something of an aversion, designed more to cushion the impact of the fist with its target than anything else. Still probably has its shades of this mainly due to the context in which one most often sees it used...