F-Zero GP Legend included a memetic punch scene in which there is an explosion comparable in size to one-eighth of the galaxy, which both kills the Big Bad and acts as a Heroic Sacrifice for the Captain (He had an Unexplained Recovery by the GBA game.note The explosion was caused by something else, but that makes it less awesome, so we'll just pretend.
In an episode of Soul Eater, Maka receives one from Black*Star of all people.
It was her suggestion, in order to make up after arguing with him.
Akane Tendo (and most of the other female martial artists) in the anime adaptation of Ranma ½. Not so much in the manga, but then the anime tended to exaggerate everything.
Also Megaton Kicks are just as common as Megaton Punches. Sometimes the target even has time to muse on the current state of affairs and smooth out their clothing while sailing peacefully through the air.
Ranma's fighting style favors speed over power, so when he needs to pull out a megaton punch, he instead punches the same spot hundreds of times per second.
Rekuta in Duel Masters. In the American dub, at least, he would be sent flying into the sky when he was so much as clipped by someone's bike.
Though it would normally follow a cry of "TODOMEDA!" from Shobu.
Even though it is not necessarily a punch (at least most of the time), Team Rocket on the Pokémon series always ends up flying into orbit (Team Rocket's blasting off agaiaaaaaaan!...*ting!*), even if the attacks that sent them weren't necessarily that powerful.
As a bonus, the Japanese name of the move "Mega Punch" is "Megaton Punch" (and it's mentioned in the second series opening theme in Japan).
Ash's Chimchar/Monferno/Infernape has something like this as its signature move. When ordered to use Dig it'll go underground, then pop up right below the opponent and punch them in the chin hard enough to send them flying. After it evolved into Monferno, doing this to Paul's Electabuzz caused an explosion.
Love Hina often used surprisingly-involved animation for these. Its frequent use by Naru Narusegawa means this trope is also sometimes known as the "Naru Punch". Again, didn't happen as often or as dramatically in the manga, but much more frequently than in Ranma ½.
In the first episode, Naru somehow manages to deliver the Megaton Punch... from the ground-level hot spring, up to the balcony where Keitaro was standing, two floors up, without her feet leaving the ground. As he flies off, Keitaro begs to know how she reached that far.
Then there's the scene where a nerd-disguised Naru punches Keitaro through a corridor with him bouncing off the walls and one doorframe (while every bystander just watches and stares without getting bowled over by him) before coming to a smashing halt at a closed door, one of many scenes that earned Keitaro his reputation of being immortal.
That was no ordinary scene; that was when they first met as adults.
It turns out that Negi's mother Princess Arika did this a lot to Nagi.
Anya also did these several times to Negi... until he decided not to let her and reality ensued, showing him to be far too much stronger for her to be able to hit him otherwise.
One episode of Tenchi in Tokyo featured Amagasaki continually trying to talk to Tenchi and Sakuya, only to be attacked by the spirit of a female wrestler. While the wrestler used a different move every time, the result was always the same shot of Amagasaki flying off into the distant city, even when he was inside.
In Magical Project S, Ramia frequently does this to her little brother Rumiya to send him to Earth.
Subverted in Full Metal Panic. Chidori hits Sagara, then the camera suddenly changes to the sky with a big contrail. This gives the impression that Sagara himself just left the contrail while crossing the atmosphere.
Simon teleports halfway through the world, rips the Gurren Lagann through a wall, ejects from his cockpit, slides across the ground for a good hundred feet, brings his hand back, and with a fantastic scream of "ROSSIU!!!!! LET'S SEE YA GRIT THOSE TEETH!!!!" he slugs Rossiu right in the face. All at once he honors fallen brothers, puts the The Scrappy of the series in his place with gusto, acknowledges Rossiu's basic decency and good intentions, and punches a man so hard his headband holding his hair in that Fei-like style explodes from the sheer ungodly awesome of the punch. Rossiu's lucky he had a HEAD after that. He INVENTED teleportation just to punch someone in the face. Gives a whole new meaning to Dynamic Entry and Get A Hold Of Yourself Man doesn't it?
In Sengoku Basara, especially in the Heroes expansion, Takeda Shingen pulls this off and sent Sanada Yukimura flying. "OYAKATA-SAMAAAAA!!!!!"
In the anime adaptation, he did it again to Fuuma Kotarou, but since the way to the sky was obstructed by a castle, he crashed there, leaving quite a hole. Also later, his Megaton Punch catches on fire and turns Hojo Ujimasa into a twinkle in the ash.
In the anime version of Naruto, Sakura does this to Naruto in Shippuuden when he's being particularly perverted. Somewhat justified by the fact that she is physically able to send him flying because she's gained super strength.
In Hunter × Hunter: Greed Island, Bisquit punches Killua this way whenever he makes a reference to her actual age.
One of Gon's special nen techniques turns his already powerful punch into a Megaton Punch by gathering all of his nen in his fist.
In Fushigi Yuugi, the Nyan Nyan girls (Taiitsukun's assistants) often ended up in the receiving end of these when they seriously screwed up.
In Tona Gura, both Kazuki Arisaka and Marie Kagura, albeit through use of her paint-ball gun, can knock Yuuji Kagura clean across a room. Very very rarely, he can even become A Twinkle in the Sky. Subverted at least once, when Marie was about to punish Genki Girl Nina Isokawa. Yuuji effortlessly disarms her, and only gives her weaponry back when he shames his younger sister into attacking only him. Fridge Logic or Rule of Funny? You decide.
Subverted in Dragon Ball Z. Hercule attempts to use his ultimate move (appropriately named the Megaton Punch) on Android 18. It doesn't work.
In the latin dub this punch has twenty words in its name.
Dragon Punch/Dragon Fist, one of Goku's moves that doesn't see much use in the main series but happens in the Non Serial Movies and Dragon Ball GT from time to time, is a full out lethal punch that, at Super Saiyan 3 or higher, makes a mini golden Shenron that explodes.
Episode 7 of To Aru Majutsu no Index II has Accelerator doing two in quick succession. First he charges at his victim and lets loose the first punch which she blocks with the MacGuffin the arc was about, shattering it. Accelerator throws off a quick one-liner and lets loose the second punch straight into the girl's face, sending her flying for over a hundred meters until she gets stopped by a wall and falls several floors down onto a grate with her face soaked with blood. Accelerator is walking with a cane and shouldn't even be able to speak, much less use his vector manipulation ability. Talk about Handicapped Badass...
THE iDOLM@STER - The Futami twins apply one of these on the Producer, calling it by name.
In the famous comic-book series Astérix, the magic-potion-powered Gauls frequently send Roman Legionnaires flying so high that they don't come down for several more panels.
In the same vein, most of the time their sandals, shields and sometimes also the complete armour stays on the ground with their owner forcibly removed, so that when the legionnaire finally comes down, he does so in underwear only.
Convenient for Obelix, who, as a result of a bet in one of the early books, collects their helmets◊ as proof of having beaten more legionnaires than Asterix did.
The video game Asterix and Obelix: XXL and its sequel incorporate this: whenever an enemy is defeated, they fly off the screen at high speed, stretching like elastic. However, only a helmet (which constitutes in-game currency) is left behind, as opposed to a full set of armour.
Alice's Fist of Death from Dilbert. Not always flying off, but she hit For Massive Damage. She once hit a guy so hard she knocked him into next week.
Garfield used to do this a lot early on to other characters who made him mad including Nermal on one occasion one punch sent him flying into the moon.
Live Action TV
Hana of Kamen Rider Den-O is capable of punching anyone through the roof of a time-travelling train. Normally, the frequent victim of this would be the Imagin Momotaros. It doesn't stop him from Tempting Fate and pressing her Berserk Button multiple times, however.
The story Sleeping with the Girls, has these as a major theme. While inhabitants of the various anime/manga worlds that the protagonist travels through are protected from megaton-punch-induced-injuries due to the Rule of Funny (which is an actual universal law in these worlds), the protagonist knows that if he is hit with that force, the Chunky Salsa Rule will be in effect for him. The reason is that he comes from our world, and since our world does not have the Rule of Funny, he is not protected by it.
Guybrush Threepwood suffered this quite badly at the end of The Secret Of Monkey Island, getting repeatedly punched into the air during his confrontation with LeChuck.
Amy Rose has her Megaton Hammer, which is useful for knocking around Sonic.
In God Of War: Chains of Olympus, if you get the Gauntlet of Zeus and level it up all the way, you can get a Megaton Punch going.
There's also the Nemean Cestus of God of War III, which lets you reel in an opponent for one.
Mega Man ZX has appropriately-named "Megaton Crush", the half-Charge Attack of Model F's Hand Cannon which can send opponent forward and hitting another opponent on the way for an extra killcount. Hence the weapon's name, Knuckle Busters.
Several of the Jack characters from the Tekken series actually have a move called Megaton Punch, which is a powerful punch that does 40 damage. In addition, there is the Gigaton Punch, which is one of the most damaging (unblockable and 199 damage, meaning it'll only not take you out if you're playing with a 100% handicap and have full health) and difficult (a "lever spin" is required to pull it off in the PS2 version, but it is never explained what exactly that is) to execute, but, yes, sends the opponent flying across the stage until they hit the invisible wall.
Roger the kangaroo and Alex the velociraptor have a similar attack, called "Animal Gigaton Punch." It's substantially easier to pull off than Jack's attack (originally just a lever direction combined with Left Punch), yet it's almost as powerful.
In The King of Fighters, Ralf Jones has a similar move named Galactica Phantom, which is practically unblockable (though fairly easy to avoid by jumping in the right moment) and, if connected, sends the opponent flying across the stage a la Megaton Punch.
It gets worse in the GBA spinoff The King of Fighters EX 2: Howling Blood, where the Galactica Phantom has a much, much shorter charge time and is a regular move instead of a SDM, meaning you can conceivably OHKO someone right off the bat with it on a counterhit...
Ryo Sakazaki has this as well, with Tenchi Haoken, which has the added benefit of STUNNING your opponent.
By luck or if you feel you're pure awesomeness, have these as a counter attack and you'll shit bricks from the damage it causes to your enemy. Especially Galactica Phantom SDM. Lethal even for bosses.
In Super Robot Wars Original Generation 2, Excellen playfully invokes this trope if you have her perform a certain mecha's punching attack, pretending that the enemy is her boyfriend being stubborn. The Original Generations remake even has her screaming out: "Kyosuke no BAKA!" as she delivers the final blow.
Seolla follows this suit when she rides the hot blood inducing machine Gespenst Mk II S. Have her execute the Gespenst Kick, and she'll pretend the enemy is Arado and yells out "A-ra-do no.... BAAAAKKKAAA!!" and delivers a Megaton Kick to the enemy.
In Original Generation Gaiden, first we have Folka's Iadabaoth which one move start with Rapid Fire Fisticuffs but end with Punched Across the Room which broke the mountain in background. Then Shura King Alkaid's Raha Exteem ditch the spam part and just punch once, send enemy through several mountains.
Guilty Gear's Potemkin has an Instant Kill in XX that fits this trope - he takes off his power-limiting collar and kills the opponent with a single punch.
In the same game, the vampire Slayer has an Instant Kill where he punches his opponent into space, turning them into A Twinkle in the Sky. Then recites a haiku.
In Primal Rage, the character Blizzard has the aptly-named To Da Moon fatality.
This is Yui's favorite move to use on Ryo in Brass Restoration. She's apparently been using it on him since childhood, so his intense training has made him immune to any damage he would otherwise suffer.
Grand Theft Auto San Andreas had a cheat which turned your standard melee punch into a Megaton Punch, allowing you to send enemies flying a hundred feet straight ahead when you punched them. For added hilarity, the cheat also affected NPCs.
Fire Emblem has one in Path of Radiance: when Boyd teases Mist for weighing more than Leanne, she knocks him across a pool of water and into a tree. The animation for the "Smite" ability, which, normally, is available only to the largest character in the game (disregarding shifted dragons), is used for this scene. The only other character to knock someone out with a shove is the friggin' Black Knight!
This is Bowser's basic attack in Mario & Luigi: Bowser's Inside Story. If done right he can punch enemies across the screen and if done wrong he trips on the enemy instead. This is also used as a Finishing Move for the Final Boss of the game, in which he manages to rival Captain Falcon himself in Incredibly Epic Punches.
In Fallout 3 the pneumatic Power Fist can actually make an enemy explode, just like this.
With enough points in the unarmed skill this can easily be done with your bare hands. Or any weapon for that matter if you take the Bloody Mess perk.
Taken to, perhaps, it's logical extreme in Fallout New Vegas. Take said Power Fist, attach a contact plate to the knuckles and connect said plate to a double barrel shotgun. Boom.
Final Fantasy VI has an enemy attack called "Megaton Punch." It instantly kills the target party member and ignores immunity to instant kill attacks.
In Final Fantasy VII, there's a comic scene during the first few hours of the game where Barrett does a Megaton Punch on one of his allies out of frustration. This sends his ally flying across the room and onto the screen.
Bayonetta has the mother of all Megaton Punches in the ending, where Bayonetta binds Jubileus, the god of her universe, with her hair, does an elaborate magical dance... and summons a gigantic avatar of herself, also from her hair, which proceeds to kiss her fist, wind up and PUNCH GOD IN THE SUN from past Neptune's orbit at faster-than-light speed. I'd say that about takes the cake...
How bad is this punch, you ask? Most of Bayonetta's hair-demon attacks have damage calculated in terms of Gigatons, with Megatons being used for the Torture Attack finishers on mooks. The final hit on Jubileus? It's measured in Infinitons!
Also, she's not summoning an avatar of herself. She's summoning Queen Sheba, the setting's equivalent to SATAN to sucker-punch Jubileus!
In the boxing arcade game Ring King, if one fighter performs a dashing uppercut while the other fighter is standing by the ropes on the left or right side of the ring, the fighter who gets hit will be sent flying out of the ring, landing somewhere off-screen, thereby resulting in an instant K.O. win for the boxer who did the uppercut.
Demon's Souls also has one right at the beginning, if you can beat the tutorial boss (who you're supposed to lose to). If you manage to survive it (which is possible, just requires timing), you then get to visit an extra area with loot, lots of corpses... and the humongous Dragon God boss from later on in the center area. As soon as you enter that area, the Dragon God roars at you, stunning you, and then Falcon Punches you right out of the room for an instakill, sending you to the Nexus anyway. Ouch. Especially nasty if wearing metal armor, as the shower of sparks gives a really nasty idea of how painful that was.
Dark Souls has the adult Mushroom People. They look fairly goofy, move slow, and up to that point you've been fighting the young versions, which are absolutely pathetic. And then they do this to you.◊
While she does it with a throw rather then a punch, Marina Liteyears, a Robot Girl with a powerful throw (to the point grabbing and throwing is her entire attack style) of Mischief Makers does this to her creator Prof. Theo each time she finsihes rescueing him due to him trying to grope her. Another villain then grabs him and she has to do it all over again.
"Freedom Force" has this with either in-game standard characters or your custom characters, it's all up to how you design the attacks. Especially hilarious due to semi-realistic physics engine, which means that lightweight opponents get sent flying higher/further from higher knockback. If you're good at balancing perks and flaws, you can have a custom character who can wield trees and buses as early as the first couple of stages, knocking female enemies across town! Also, the physics engine applies impact damage when they land/collide with stuff. My favourite part of a really fun game.
While quite of a few of the fist attacks in the Disgaea series would qualify, the Rising Dragon fist skill in 2 and 3 is probably the best example, as it has the user do a flying uppercut on the target that brings both out of the atmosphere before punching the target so hard that they become a twinkle in the blackness of space instantaneously.
The version of it used in 4 is noticeably different in execution, but still very much a megaton punch. The victim is first punched under a waterfall flowing from the top of a mountain, then uppercutted so hard that the force sends the water flying back up the mountain along with the target. After the target flies out of sight, the mountain splits in half and crumbles to dust.
Digimon World has Megaton Punch as an actual attack that your Digimon can learn.
In the ending of Batman Arkham Asylum, Batman finishes off the Titan-mutated Joker by spraying his fist with explosive gel and punching him in the face.
The early FPS/RPG Strife combines this with Ludicrous Gibs. Stamina implants improve both your hit points and your punch damage, with enough you smash an enemy across the room in a shower of meat.
A good Wrestler in Dwarf Fortress can punt an enemy quite far away with just one punch.
In the game Super Mario Galaxy 2, Bowser actually tries to punch the planet Mario/Luigi is standing on during all three of his boss battles.
Pokemon has the move Mega Punch, which was called Megaton Punch in Japan. There's also the similarly named "Mega Kick".
In Mortal Kombat Trilogy, Rain has a move that lets him roundhouse kick his opponent so far across the screen that they coming flying back on the other side. Subverted by the fact that the distance it sends the opponent is far more than the damage it does.
Also, one of Raiden's fatalities is an explosive uppercut that blows his enemies into pieces.
Rare first person shooter example: Dark Forces, the first entry in the Dark Forces Saga, leaves Kyle Katarn with only his fists as his Emergency Weapon (this being before they established Kyle as an active Force-sensitive Jedi). Typically, punching a (humanoid) opponent puts them into a moment of stunlock and bounces them a bit. However, if Kyle crouches, looks up slightly, and punches, he can send most Imperial cronies flying across the room with greater Knock Back than all but his most powerful explosive weapons. This can get entertaining in some levels, allowing Kyle to punch stormtroopers off cliffs and the like.
Saints Row 2 gives us the highly entertaining Pimp Slap weapon. The game's loose association with reality only makes it all the more amusing to watch.
Saints Row The Third upped the ante with the Apocafists, giant rubber fists that send cars flying and turn people into showers of blood.
Mass Effect 3 introduces class-unique heavy melee attacks to the series. While most classes use omni-blades and the Adept focuses on Punched Across the Room, the Vanguard class gets a straight-up powerful biotic punch which executes faster than other heavy melees, synergizing well with their Charge ability.
And now the Batarians join in with their Omni-gauntlets. One punch, and Your Head Asplode. The addition of batarian Vanguards makes this even better.
In spite of the Bayonetta example above, There isan even more powerful example of this. Asura from Asura's Wrath does this on a regular basis, from punching out a planet sized deity's finger and making him explode with one final punch, all the way to growing bigger than the planet itself and punching straight through the Creator of life's forehead, all the way to doing multiple Megaton Punches with the final one killing the Creator's ultimate form, even at the cost of his life.All for the sake of his daughters safety.
In the Marvel vs. Capcom games, Jin Saotome's Heavy Punch attacks tend to be more Megaton than Fierce as it is. But he takes the cake with his Super, Blodia Punch: Jin punches the opponent as hard as he can, followed almost immediately by the fist of his Humongous Mecha.
In the Source engine, damage in excess of what is required to kill a player is translated into force on the corpse. A critical punch from the Heavy can launch people across a room, or a map, if their health is low enough. This is also why the Spy's Back Stab tends to launch ragdolls around on a whim, because all backstab kills are triggered by absurdly excessive damage rules.
Umineko no Naku Koro ni: At the climax of Episode 8, Battler Punchesout Bernkastel. Bernkastel who, just scenes ago, had been laughing off universe explosions. Battler's fist is more powerful than the universe. And inflicts the concept of pain.
Pick a Popeye cartoon, and half the time, after pummeling the bad guy into a bruised, battered shell of a man (or woman... or alien...), Popeye will deliver one last, huge punch, often with humorous results upon landing.
In Justice League Unlimited, taking a punch from one of the more powerful characters easily sent the victim several miles or further (this is probably what is expected, considering some punches are capable of breaking the sound barrier).
Best example is when Superman delivers a punch on Darkseid. This is after Superman gives his "World of Cardboard" Speech and reveals he's ready to cut loose on the one person in the universe he can hit at full power...
To put this in perspective, with one punch, Darkseid was sent sailing through seven skyscrapers, and kept going! The only thing that stopped him was Superman giving him a Meteor Move midflight.
In Regular Show even the weak can do this practising the art of "Death Kwon Do": wearing a mullet and cut-off jeans.
In an episode of The Angry Beavers, Dag picks on his brother everyday until finally, Norbert gets so furious he litterally punches Dag into last week...repeatedly. Finally, Dag ends up making him promise not to do it again, then accidentally ruins the end of his movie by spoiling the ending. Norbert keeps his word and doesn't punch him into last week. Instead... well, this quote will explain it.
Dag: *looks at the calendar* Hey...he didn't bop me into last week! *looks outside the window* Eeeh. If I may borrow a phrase from my brother Norbert....HE BOPPED ME INTO THE DAWN OF TIME!!!
Hack and Slash from ReBoot were capable of this, although they rarely got to show it since they were usually too busy putting the "dumb" in Dumb Muscle. In the episode "Gigabyte," after Hack is drained of his energy by the titular character, Slash gets revenge by unleashing a seriously epic Megaton Punch, knocking him from outside Mainframe right into the heart of the city... which is where Bob was trying to keep him away from.
In case you missed it, they were checking to see if Walcott was alive. That's the kind of punch that makes Captain Falcon look like a pansy.
The punch of the "smasher" variety of mantis shrimp has an acceleration of over 100,000 m/s2. Not only is the impact of the punch itself incredibly powerful and has been known to break through aquarium glass with a single strike, the rapid acceleration (about the same as a .22 caliber bullet) actually creates a shockwave from the collapse of cavitation bubbles, capable of stunning or killing its target even if the punch itself misses. Watch this specimen break open a clam, and just listen to those blows. The sounds are being muffled through aquarium glass. The shockwave is also accompanied by a small burst of light and a temperature increase of several thousand degrees, although the effect is too short-lived to have any real offensive significance.
Bruce Lee had a finger-hand punch - his famous "one-inch punch" - that moved so fast and was so powerful it would knock back opponents several feet. Even when the opponent was ready for the blow.
Dan Henderson is known for (what is in many people's opinions) the hardest knockout punch in mixed martial arts (MMA) history. Henderson knocked out Englishman Michael Bisping at UFC 100 with a punch he wound up almost 180 degrees and stepped into with most of his body weight (Bisping was also circling into the punch). "Hendo" followed up the sledgehammer blow with an equally-devastating full-body-weight-jumping-elbow to Bisping's face after the poor Brit had already hit the ground, unconscious.
At about 0:08 in this video of prison inmates saving a prison guard from being strangled, the first Big Damn Hero charges forward and throws all his momentum into one punch, before dogpiling the strangler with other prisoners. It is just as awesome as it sounds