The protagonist I Did Not Want To Die sacrifices himself to save his comrades from pursuing enemy soldiers after he is mortally wounded. He manages to kill a good dozen opponents before he is finally taken down, and he still has one grenade left...
Downfall gives us this in the second battle of the Rukongaki. Renji, Rukia, and Kien are faceing off against Aaroniero, wearing Miyako Shiba's face. One by one they fall, wounded, until it's just Rukia and the abomination. Rukia is dieing, bleeding out, covered in horrific burns and demoralized with guilt. How dose she go out? Driveing a sword through his skull, and becomes the first Soul Reaper to kill an Espada in the course of the war.
In Broken Bow, Armani willingly allowing his entire being to be erased to save the world from becoming a literal hell because a breach in the walls of reality that was anchored on his blood was going to bring in the most powerful forces of horror from every universe ever... Yeah, I'd say that qualifies.
He just got knocked into Artemis Fowl's universe, and got back... eventually. He did have to steal the crown jewels to do it.
In Team 8, Itachi is forcing Kurenai to watch her greatest fear via Tsukiyomi: her students getting lynched for being associated with Naruto and the Kyuubi. She breaks free by forcing the situation into its logical outcome (Naruto going on a berserk rampage and killing everybody). The illusion is too much for Itachi to hold, meaning Kurenai broke free of the Mind Rape through sheer will (although it should be mentioned that this is not how Tsukuyomi works in canon). Unfortunately, Itachi immediately realizes what a threat she is if she can resist Tsukiyomi and promptly throws a kunai into her skull.
In Divine Blood Hild, weakened by the crash of Nidhog, still manages to destroy several demonic mecha stated as being weapons the equal of a fully powered category 1 demon along with several big name demons among the released criminals and rebels. Eventually, she obliterates an approximately two mile radius of Nifelheim. The rebels, stalk forward to confirm she died in that blast and are on the point of celebrating their victory when she manages enough energy to look at them all and say "Boo." before her life gives out. This is enough to trigger a stampede away from her in which some demons are implied to be at least injured in the press to flee. It is later stated that she took out half of the enemy forces this way.
On top of this, she died on her feet, being an example of a "standing death". Expending so much energy and putting so much strain on herself that she went into rigor mortis in the last moments of life.
Duncan gets one in Dragon Age The Crown Of Thorns. When he and the DN get cornered in Ostagar, not only does he haul the protagonist off the fortress's ledge and shield him with his body from the fall, smashing his back (and ending up paralyzed and with bad internal injuries) in the process but, later, after said dwarven noble carries him away from the battle (and Duncan had been telling him to leave him behind), Duncan pushes him out of the way of a blight wolf's sneak attack and takes it himself. And he still survives enough to tell him that only Grey Wardens ca kill Archdemons, although he doesn't manage to explain why and how it's done.
Takato from the Tamers Forever Series has an absolutely EPIC one. He takes on a hoard of Mega level digimon, even though his clothes are soaked in his own blood and he is almost paralyzed due to his brain cells slowly dying off.
According to a Hellsing / Cthulhu Tech crossover entitled Old Blood Integra had a particuarly awesome one, being killed at the age of eighty-six after forcing her way into the command centre of the Nazzadi during the initial siege via just telling them to bring her there and then killing the top three officers on the scene with a sword hidden in her cane. Her body was later cremated and half the ashes were mixed with nerve gas used in an attack that took out over ten thousand Nazzadi. As one commenter put it, "Sir Integral Fairbrook Wingates Hellsing. She died as she lived. That is all that needs to be noted."
In Ace Combat The Equestrian War, Blueberry fought against four griffin soldiers and managed to defeat one of them, refusing to surrender, before being killed, as reported by Flare Star. Her team recovered Blueberry's body from the battlefield and brought it to the Canterlot Castle so they could give their honors.
During the "Origins" arc of the Pony POV Series, Mimic pulls a You Shall Not Pass on Discord in order to give Celestia, Luna, and their allies time to escape. After triggering a Villainous Breakdown in him by explaining that the rainbow bridge between Ponyland and Earth has been destroyed (thus denying him the chance to torture humanity when he's done with the ponies), she proceeds to kick him in the face several thousand times at the speed of sound, which proves he's not as Nigh Invulnerable as he appeared, as she manages to permanently knock out his tooth, which is what pisses him off enough to finally kill her. For bonus points, she was Celestia and Luna's mortal mother, so this was her going Mama Bear on his flank.
The Dark World arc reveals that the Epilogue timeline version of Cadence went out with a bang. When Discord and his enforcers — the discorded Mane Six — launched a final assault on her, she bought time for her subjects to escape by taking them all on. And she wins — she actually manages to scare Discord off, and defeats all six of the corrupted ponies, even managing to purify Twilight in the process. Unfortunately, Discord chooses that moment to return and literally stab her in the back, before disintegrating her. Then to top that, her spirit returns five hundred years later and redeems Twilight.
Surprisingly, Dark World Discord gets one. His last act before dying is to convince Twilight to perform the Memory Spell on him, allowing her to see his memories of the "Groundhog Day" Loop he's been trapped in. This ends up Out GambittingNightmare Paradox's plans and exposing them to the Elements of Harmony, which allows them to break free of her influence and fight her.
In the early loops of Dark World, including the first, Apple Pie died in a Heroic Sacrifice, distracting Discord so Twilight's plan to reset time could work, managing to break his horn off before being brutally murdered by the enraged tyrant. Unfortunately, that Twilight was the one who became Nightmare Paradox, causing her to turn it into a Senseless Sacrifice.
Another early Dark World loop, apparently involving Trixie becoming an Alicorn, had her, presumably before being killed, managing an attack on Nightmare Paradox's face, leaving a Wound That Will Not Heal on her face in the shape of Trixie's cutie mark, requiring Paradox to weak a White Mask of Doom from then on, regardless of how many loops it's been since then.
The climax of the Shining Armor Arc has several: (all of which are undone by Cosmic Retcon at the end)
In the actual Final Battle, Gilda is mortally wounded by Makarov, but just before dying she uses the last of her strength to destroy his Iron Curtain, thus allowing the Wolf to defeat him (thus triggering the above Cosmic Retcon).
In Part 1 of Clash of the Elements, even though Zeno Blaze is the last to die against Joe Dark, he goes out not only performing a Shut Up, Hannibal! to him, but summoning a large pillar of flame against him even though he knew it wouldn't harm him.
Alex Whiter's Heroic Sacrifice against Chaos Alex
In Naruto and the Last Vampiress, Naruto pulls something like this off, stabbing Shukaku's Tailed Beast Ball with the White Chakra Blade, saving Sasuke. Anko turned him into a Hanyou after this, but it was his human death
In Harry Potter and the Altered World, most of the people who died in the bad future before Harry timetravled and altered the time stream immensely, among the best examples are Luna, who had her soul removed by a Dementor, saving several lives including Susan, and Neville, who died holding off purebloods to allow Harry to time travel. Its also said that this future was caused by Purebloods taking Voldemort's canon death as this trope.
In The Things We Leave Behind, Twilight Sparkle dies saving Ponyville from an Ursa Major, unleashed on the town by a vengeful Trixie. Specifically, she casts an age reversal spell to reduce it to an infant, using up so much of her magic in the process that she has to resort to drawing power from her Life Force to continue. She never stops until Ponyville is safe.
Might Gai in A Growing Affection. He and Kisame have kept "switching hands", until Kisame breaks out his six tails cloak (in this fic he is host of the Seven-Tails). After flashing back to explaining to Lee how it works, Gai opens the Gate of Death, and proceeds to curb stomp Kisame. Kisame starts to unleash the full power of the Seven-Tails, but Gai says he would like to let Kisame do that, but he doesn't have enough time left. So he kills Kisame mid transformation. Then Gai fades out too, but as he goes, he has visions of what his life could have been.
Death Note Equestria has one that's sadly offscreen: When Mer tried to coerce the Apple family into becoming the Third Kira, Granny Smith refused to let her grandchildren become killers. As AJ puts it, she stared down a God of Death and said no. This got her killed, but it's still awesome nonetheless.
Klaus gets in the finale of the Jill Gilbert Saga, he takes a stand against the Balcoin Circle, who easy defeat him, but succeeds in distracting them long enough for Jill to kill one of them and save the world.
The Mission Stays The Same gives one to the Eldar civilization that inhabited the Mass Effect universe many cycles ago; the Reapers felt that they were developing along lines that would threaten the cycle, so they sent a small fleet to harvest the Eldar (at that time in the middle of their industrial age). The fleet never returned, so a larger fleet was sent. The Eldar had managed to defeat the first fleet and advance their tech level considerably and their psychic powers allow them to No Sell the Reapers' attempts at Indoctrination. The losses inflicted on the Reapers was such that Harbinger opted to exterminate the entire Eldar race, as harvesting them wouldn't be worth it. The Eldar gave the Reapers one last "Fuck you" before dying when they poured their psychic powers into the system's star, causing it to go nova and wipe out all trace of Eldar civilization and quite a few Reapers.
The God Empress Of Ponykind: Commander Icewind, wounded and cut off, charges right into the heart of King Sombra's forces in order to buy time for Fell-Hoof to get word to their allies, killing many before he is overwhelmed. When Sombra tries to scavenge his armor to reverse-engineer it, the Self Destruct Rune activates, blowing up the entire Plaza.
Dawn Sparkle duels Nightmare Moon in single combat during the Siege of Manehattan. She's just a normal pony versus a Mad God, and she manages to land a few hits before being cut down. Sadly this is all offscreen.
Remember how Pain stated that if Jiraiya knew his secret from the start he probably would have won? One Naruto fanfic proves it. Jiraiya has more information on Pain (due to Konan pseudo-defecting) and figures out where the real Nagato is much faster. He destroys six of Pain's bodies and would have killed Nagato as well if not for Tobi warping himself and Nagato away. Even better his death activates a scroll he hid away earlier, releasing Itachi's Amaterasu that he'd sealed away years ago, burning down Pain's base in Ame.
In A New Order this is the fate of Shadow Warrior Tethys. After pushing the senshi farther than any enemy before (in a fic where Sailor Moon repeatedly one-shots youma) she calls up a huge mass of water that would have swamped the cruise ship they were on, had not Mercury and Moon teamed up to take her out with two brand-new spells. They both pass out almost immediately after, meaning the senshi would have been in trouble if she had survived that, too.
In MLP/Fallout:3 Fic Wandering Moon, Archmage Clover gets a great one. She singlehoofedly goes up against a giant Ursa Major and not only beats it soundly, but does so in her late 80s before finally dying of magical exhaustion.