In the season 1 finale of Avatar: The Last Airbender, Princess Yue sacrifices herself to revive the Moon Spirit, which had been killed by Admiral Zhao. She then becomes the new Moon Spirit. Though in this case she had been living on borrowed time her entire life, as the Moon Spirit had shared some of its life energy to prevent her from being stillborn, and she simply gave it back.
Also, at the end of season 2, Iroh stays behind in the caverns fighting Zuko, Azula, and all of the Dai Li to buy time to allow Aang and Katara to escape to safety, even though he knew he couldn't escape himself.
In season 3, it is revealed through flashbacks that Katara's mother Kya lied about her daughter being a water bender, instead saying it was her. Her last words to Katara were "Everything will be all right." She was lying. However, she was expecting to be taken captive instead of killed, though it's no less admirable.
The Sequel Series, The Legend of Korra has a non-fatal example when Lin allows Tenzin and his family to escape the Equalists by taking down the airships,only to be de-bent
And the much-more fatal example in the finale with Tarrlok blowing up the boat he and Amon are on. Doubles as Redemption Equals Death, possibly for both of the bloodbending brothers if one interprets Amon's Single Tear as a sign that he knew what Tarrlok was about to do and didn't try to stop him.
Does this in order to save his friends in "Coon vs. Coon & Friends" by impaling himself on a pit of spikes in order to escape the Eldritch Location Cthulu banished them to, knowing he'll wake up in his bedroom so he can find help from the Goths.
And in the episode "Jewbilee" after various attempts at freeing Moses from the conch shell failed while Garth who had betrayed the rest of the Jew scout masters was going to release the evil spirit Haman, Kenny then smashed his skull over the conch breaking and freeing Moses, he dies from the impact in the process
Also enforced by the Anit-Smoking group in Butt Out when they have Cartman shoot a commercial where he says he was stage 4 lung cancer. It's very-nearly name-dropped by Rob Reiner during his "Do you know what a hero is?" speech to Cartman.
Bwana Beast destroys himself at the end of Starro's invasion to save the planet.
At the end of one episode, the Doom Patrol sacrifice themselves to save an island of people.
In "Long Arm of the Law!" Plastic Man lets himself get turned into stone when promised that it will keep his family safe. Because Kite Man is Chaotic Evil, he releases the hostages... into the open, stormy sky, stuck to a kite. However, Plastic Man's sacrifice is ultimately reversed in time for him to save them.
In the 2nd episode of Ben 10: Alien Force, the plumber agent saves Kevin's life, but tears his suit - since he doesn't breathe air, he dies. This is considered part of the reason Kevin agrees to help Ben for the rest of the series.
Kevin's father, Devin Levin, jumps in front of a lethal blast to save Max Tennyson from Ragnarok.
In Code Lyoko, Aelita is sometimes a bit too eager to make a Heroic Sacrifice, despite the very strong disapproval of her friends (especially Jérémie). She actually went through it in Season 1 episode "Just in Time", but Jérémie managed to bring her back to the virtual world. Another close call was in Season 2 finale "The Key".
In the end, her father, Franz Hopper, made the Heroic Sacrifice to destroy XANA, his creation, once and for all.
The Fairly OddParents "Wishology": Jorgen Von Strangle and Timmy Turner. Jorgen, in the first part of the trilogy, magically transforms himself into Timmy so the Eliminators and the Darkness do not take Timmy. Timmy at the end of the second part when he throws himself up into the Darkness so the group of people he is with are not hurt or captured. This is especially significant because in addition to his family and friends being in the group, three are his mortal enemies and four are magical fairies who are almost impossible to kill.
Near the end of "Love and Rocket", he realizes that Leela's oxygen tank is empty, and that she is too busy fixing the ship in order to save the lives of the crew to listen to his warnings. He then plugs her tube into his own full tank and nearly suffocates, saving her life in the process.
Leela: *reading off a candy heart* "U leave me breath-less!"
When confronting a getaway Space Bee in "The Sting", Fry throws himself in front of Leela so the bee would sting him. It didn't quite work out that way...
"The Why of Fry" involves Fry infiltrating a Death Star-like Brain Spawn station with the almighty Niblonian's vehicle of choice—a "Scooty Puff Junior"—gambling on being condemned to an eternity in oblivion than risk Leela's safety in the end. Good thing Nibbler remembered Fry's little bit of advice: "Scooty Puff Junior sucks!"
Fry did this yet again in Bender's Big Score.Well, not quite him. Lars, his time clone, broke up with Leela when he realized it would cause a Temporal Paradox, killing him in the process. Upon the original Fry's attempt at reconciling them, Nudar holds Leela hostage. Knowing his life is going to end one way or the other, he kills himself blowing Nudar up with a self-destructing Bender clone.
Also, in "Into the Wild Green Yonder", Fry realizes that he is "the Dark One" who he has been pursuing and must kill in order to save the galaxy. Fortunately, his logic was flawed (as per usual) and he survives and also kills the real Dark One.
Cannon robot Big Bertha in "The Prisoner of Benda," sacrificing herself to help the Professor save Emperor Nikolai by compromising the last of her structural integrity with one last Human Cannonball.
Professor Farnsworth: (in Bender's body): But you could get a new body. You could have a rich, full life!
In The Mighty Ducks' first episode, Canard throws himself into dimensional limbo to save the rest of the team and allow them to pursue Dragonus to Earth.
Also, in the episode "The Final Face Off", Wildwing destroy Dragonus' dimensional ray to prevent the Earth from being invaded and conquered by the Saurian army, even though he knows that the dimensional ray was the only way he and his friends could return home to Puckworld, and as a result they are now permanently trapped on Earth.
Later attempted in the season one finale when Gene pushes Pepper out of the way of Fin Fang Foom's attack and is apparently killed. Ironically, his heroic sacrifice is what allowed him to acquire the fifth Makluan Ring and then betray the very friends he was helping
Codename: Kids Next Door: in what is possibly the only existing example without any possibility of physical injury, Tommy Gilligan (Numbuh 2's brother) has just been assigned to Sector V. He saves the sector, and the whole organization, from being turned into animals by the Big Bad. However, by removing his DNA from the registry he is not allowed to be part of the organization, even though the others (who had never liked him) now believe he should be.
In King of the Hill, Bobby becomes covered in a swarm of angry, venomous fire ants that cover their victims and kill them by all biting at the same time. However, Dale grabs his hand, allowing the ants to swarm onto him instead (Dale is an exterminator, and the ants have a grudge), whereupon they proceed to all bite him at the same time, nearly killing him. He gets better, though Hank first has the opportunity to cradle him in his arms and thank him for saving his son.
In ReBoot, Hexadecimal, after her Heel-Face Turn, in order to destroy Daemon, fragmented herself in order to administer a cure to the Net.
And just before doing that, gives little Enzo a parting gift that alters his icon so that when he touches Nibbles again, its mind is restored and Wellman Matrix returns to Mainframe... well, as a null, anyway.
In Superman: Doomsday, an internally-injured Superman, seeing Doomsday about to murder a child for the fun of it, flies him up past the atmosphere and then gives him the biggest bodyslam in history. The impact kills Supes, too. If only for a little while.
Dinobot, in the Transformers: Beast Wars episode "Code of Hero", fights the entire Predacon force on his own to prevent them from altering history. He drives them off, but is mortally wounded in the process.
Luckily for him though, he got to die as he lived — quoting Shakespeare.
There's also Omega Supreme, much to Ratchet's dismay. He sacrifices himself heroically twice, once offscreen, in the Great War, and the second time in the same episode he's resurrected in, this time to protect the Autobots from the blast of the malfunctioning space bridge. The mech's the embodiment of this trope - he's made to sacrifice himself if need be!
Arguably, Bumblebee in "Autoboot Camp" might qualify, although it is non-fatal. He does, after all, take the blame for a tower falling on his Drill Sergeant, Sentinel Minor, to protect Bulkhead from being drummed out, since Bulkhead saved his life when the spy in the camp replaced the paint in the weapons used for a training exercise with live ammo. After he's (supposedly) caught the spy, and Sentinel has told him that he's Elite Guard material, Bumblebee gets drummed out instead. Sentinel is a real Jerk Ass.
Earlier, Bee took a hit for Bulkhead when he was about to get hit by Meltdown.
And now there's Prowl letting himself be absorbed by the Allspark to give it enough strength to stop the Omega Supreme clones, which are rigged with bombs, from destroying everything in a hundred-mile radius, drawing tears from every fan watching.
In the Japanese Transformers: The Head Masters, Optimus sacrifices himself to stabilize Vector Sigma at the beginning of the season. This is his Final Death of the series, at least in animated form (there was later a toy line and manga called Battlestars: The Return Of Convoy, where he was brought Back from the Dead).
Wolverine and the X-Men gave one to a Sentinel named "Rover." Best friend to Marrow and only able to say the word 'destroy' with varying degrees of emotion. To get the information to stop the Bad End Rover gets into a fight with five evil Sentinels. Buying time for Professor X and the others to get the information needed and escape. He's being destroyed by a bunch of tiny wolf-like sentinels, his last word is to his friend Marrow, "Run."
In the episode Legends, a few members of the Justice League get transported to a bizarre Golden Age/Silver Age-style alternate universe where various cornball heroes and villains battle over Seaboard City. After The Revealthat the whole city, heroes/villains and all, was a Lotus-Eater Machine, the Justice League attempts to fight the true villain, but they lose badly. They're saved by the local heroes, the Justice Guild, who charge into battle despite knowing the villain's defeat would result in a Dream Apocalypse that would take them along with it.
"We sacrificed ourselves once to save this world. We can do it again."
The Flash from Justice League Unlimited in the episode Divided We Fall. It's the league's Darkest Hour, and the founding members are down. The Flash built up energy by running circles around the planet and culminated with using the energy to defeat Luthor in an explosion. Because of this, he sort of phased out of reality. He got better very quickly.
Near the end of the fourth season of Winx Club, Nabu decides to try to close the shadow abyss in order to save the Earth fairies. He succeeds, but uses up all of his energy and dies as a result.
In Monsters vs. Aliens, it's not death, it's something worse. The whole movie is Ginormica just wanting to be plain, normal Susan Murphy again. Then the alien extracts the phlebotinum from her, making her normal-sized again. In order to save the planet, she drops the quantonium on herself, turning her back into Ginormica permanently.
Galaxy Rangers loved this trope. At least four examples in the series, starting with Eliza, who ordered the ship with her kids to blast off, leaving her to a Fate Worse Than Death.
In The Brave Little Toaster, Lampy, Kirby, and Toaster all pull this off. Respectively by allowing himself to be struck by lightning, jumping off a waterfall, and jumping into the gears of a trash compactor to jam the machine. They all get better, but the "deaths" of Lampy and Toaster were traumatizing, as the viewer probably believed they actually were dead for a few minutes.
Radio also did this in the sequel by giving up his function tube in order to save their obsolete super computer friend, and seeing as how they needed him to save their animal friends, it counts double. Considering that it was because of him that the only other tube broke, it was the least he could do.
Van Rook of The Secret Saturdays jumps in front of an energy beam intended for Drew. It was the first (and sadly last) truely heroic thing he ever did.
Black Panther does another one in order to help the team stop the Kree Empire, complete with a somber speech to his comrades. He's revealed alive in the next episode, apparently having been accidentally teleported out of his space ship seconds before it exploded.
Suprisingly, Regular Show has had some truly heroic ones. In "Benson Begone", Benson prepares to perform one to save everyone from the demonic Susan by running her down with a limo, only for Leon, a character from earlier in the episode, to jump into the limo. He then pushes Benson to safety and takes out Susan's heels, causing her to fall back into Hell while he spirals out of control and crashes into a wall, the limo exploding on impact. A second one happens in "Go Viral" where the episode's Big Bad, the Warden of the Internet, tries to kill Mordecai, Rigby, and Pops to stop them from escaping her cyberspace prison. Suddenly, one of the other viral videos she captured, the Wedgie Ninja, grabs her and gives her a wedgie, telling the others to run. After they escape, he keeps it up and eventually causes the Warden to explode, killing himself in the process but making the Internet safe for viral videos once more.
Parodied in "K.I.L.I.T. Radio" when it looks like Donny G was killed in the destruction of the radio station, only to appear at the end next to Mordecai and Rigby. Coincidentally, it's the second time he survives a fatal incident in the episode as before the station blew up he had a laser go through his chest.
In The Simpsons, it's revealed that Waylon Smithers Senior went into a nuclear reactor core unprotected and turned it off, in the process giving his life to save Springfield, everybody at the plant and Waylon Smithers Junior. One of the few times Mr. Burns shows any respect for any character in the series.
Teen Titans character Terra does this. Her power is manipulation with the earth (hence her name). In Season 2 finale a volcanic eruption is set in place under the city. Terra uses her power to stop, and seal it, but the price for doing so is her turning to stone.
Red Torpedo and Red Inferno do this in Young Justice, sacrificing themselves to destroy their crazed "sibling" Red Volcano.
In the Season 2 Finale, Kid Flash sacrifices himself to help the Flash and Impulse stop the Reach's endgame, as his slower speed made him vulnerable to fatal discharges of energy from the explosion they were trying to prevent and caused him to disappear, or "cease".
The tie-in comic had a nameless female gargoyle (called "Sacrifice" in the script) who took a barrage of arrows meant for her mate.
Phineas and Ferb has the two-part "Where's Perry?" special, where after one of Dr. Doofenshmirtz's inators causes Carl to undergo a Face-Heel Turn he creates Evil Knockoffs of the Flynn-Fletcher family and several supporting characters. In an inversion of A.I. Is a Crapshoot, Robot Candace feels sympathy for her organic counterpart, who at the time was having a Heroic BSOD because she thought Jeremy broke up with her, as the former doesn't have her own Jeremy and convinces the latter to get out of her fugue. Robot Phineas then attempts to kill Candace, only for Robot Candace to jump in front of his laser to absorb it, then she retaliates and destroys him.
Adventure Time: "Sons of Mars" has Abraham Lincoln, God Emperor of Mars sacrifice his immortality to revive Jake, who was wrongfully executed.
The Alternate Universe shown in the fifth season premiere was not devestated by the Mushroom War, as Simon Petrikov, before he could become the Ice King, stopped the mutagenic bomb that would have created The Lich, dying in the process.
Angel Dynamite—a.k.a. Cassidy Williams of the original Mystery Inc.—had a hot/cold relationship with Scooby Doo and the current Mystery Inc. due to her hidden ties with the old group and keeping it a secret. In episode 37, she has an uneasy alliance with the gang in tracking down Germanic robots that destroyed her radio station, leading them to an undersea fortress that was Crystal Cove's original settlement. Cassidy stays behind to ensure the gang escapes safely as the Big Bad, the evil parrot Professor Pericles, sets off bombs. Cassidy did not survive.
In episode 51, Pericles holds Marcie "Hot Dog Water" Fleach (Velma's one-time rival) hostage if the gang doesn't cooperate in opening the gateway to the hidden treasure. Marcie escapes and takes Pericles hostage so the gang can go in first and destroy the Nibiru curse. But after Marcie is sneak-attacked, Pericles turns his Kriegstaffelbots on her. As the gang have entered the gateway and are crossing a bridge, Velma and Scooby-Doo hear gunshots. Scooby turns and whimpers, as Velma sadly tells him to move on.
Both instances are subverted at the end of the Grand Finale (episode 52) as the Nibiru Entity's curse and influence are erased when Scooby destroys its power core. Cassidy and Marcie are alive and well.
In one episode of Mighty Max "The Magnificent Seven", Max and company gather a band of legendary heroes to assault Skullmaster's lair and destroy the Crystal of Souls. One of them, Hanuman the Monkey King, spends the entire episode complaining that he doesn't want to be a hero again and derides Virgil's claims that being a hero is his destiny. In the end, he sacrifices himself to save Max from Skullmaster, his final words being "It is...my destiny." The other heroes eventually follow suit, buying Max and his friends enough time to escape.*
X-Men: In the episode "Bloodlines", Mystique does the ONLY UNSELFISH THING IN HER ENTIRE LIFE; she pushes Nightcrawler aside and takes the bullet meant for him when her other son Graydon Creed tries to shoot them both.
Randy Cunningham: 9th Grade Ninja: in one episode Randy grabs the Sorceress, who was about to attack everyone at a party, and he drags both of them to the Land of Shadow, then it's subverted when Howard grabs Randy's hand and pulls him out.
In Annabelles Wish, when the titular character learns that Billy will be taken away from the farm unless he regains his voice by Christmas, she gives up her own ability to talk forever so he can.
In Tarzan, Kerchak rushes to Tarzan to protect him from Clayton after he shoots Tarzan in the arm.
Picked up in Frozen, Anna sees Hans about to kill Elsa, she steps in front of her to stop him — just as she freezes solid, shattering Hans's sword. Making it even more of this is the fact that Anna does this for an "act of true love," instead of trying to get a kiss from Kristoff, which would save her life but cost Elsa hers.