His evil clone Dinobot II has a sudden Heel-Face Turn in the Grand Finale, destroying the control panels of the Nemesis and going down the ship to a (second, sorta) death. In the same episode is Tigerhawk, who tries to take on the entire firepower of the Nemesis by himself. At first he holds his own pretty well, but Megatron turns the firepower of the ship Up to Eleven, which ultimately destroys Tigerhawk. This actually helps lead to Dinobot II's Heroic Sacrifice because he accosted Megatron for using the entire firepower of the ship on a single Cybertronian, but Megatron ignored him.
The episode right before the above had the final confrontation between Depth Charge and Rampage, in which the former impales the latter. The quote speaks for itself.
Depth Charge:"Raw Energon! Right through your twisted spark! TAKE IT! Take it straight to the Pit, YOU SICKENING PIECE OF SLAG!"
From Justice League Unlimited, Lex Luthor sacrificing himself to stop Darkseid moments before the latter was about to kill Superman. How does he do this? He gives Darkseid the one thing he really wants: The Anti-Life equation, which devours the two whole. What makes it awesome is his demeanor.
Lex:"As much as I'd like to see that, first you have some business with me. Sorry I'm late, I had to get my power suit." Darkseid: "You would challenge me? Insanity." Lex: "Oh no no no, I'm not here to challenge you, Darkseid. I'm here to give you something you want. The ONLY thing you want."
Barely averted. Batman saves his fellow crew, gives them "It Has Been an Honor" quote and plans to sacrifice himself piloting the Watchtower straight into the doomsday weapon. If Superman didn't save him at the last second this would have fit this trope to a T.
As for the guy who had the doomsday weapon installed, Hro Talak, commander of the Thanagarian forces who invaded Earth. Say what you want about the guy, but don't call him a coward. After the defeat of the Thanagarians on Earth, the Gordanians had entered Thanagarian space, but Hro Talak decided to make a Last Stand wiped out twelve Gordanian battleships almost single-handedly, and when his command ship was on its last legs, he had his crew escape on a small pilot ship while he rams his dying ship into the charged cannon of the Gordanian flagship, destroying it and several Gordanian ships in the process. Unfortunately, as awesome as it was, it was a Pyrrhic Victory- Thanagar had already lost the war.
And, after he dies Ray becomes a star beside Evangaline, the star he confused for a firefly and fell in love with. Tell me that's not awesome. I dare you.
Captain Marcus from Exo Squad, diving the disintegrating ExoCarrier Resolute into the heart of the enemy fleets to take as many of them with him as he could, and give a chance for what was left of the ExoFleet to escape. Never mind the whole situation was his fault for blatantly walking into a trap.
"Go back and tell Winfield to watch! Tell him Matthew Marcus knew how to die."
We don't actually see it, but in Avatar: The Last Airbender it certainly seems Aang's mentor Gyatso went out with a bang; his body is discovered surrounded by the corpses of quite a few Fire Nation soldiers. Especially considering he's an Airbender—a discipline which Word of God has stated is bereft of fatal finishing moves—and his death occurred during the passing of Sozin's Comet, which boosted each and every one of those firebending soldiers' powers to ridiculous levels. In order words, he took out the multiple number of troops that killed him, whilst they were at their absolute most powerful, using the least aggressive form of bending. Ask him again why he's a Master airbender.
Lin Beifong: Whatever happens to me... Don't turn back!
Likewise with Hiroshi Sato. After several years in prison for his crimes in Book 1, he gets a chance to reconcile with his daughter and help her bring down Kuvira's Humongous Mecha by co-piloting a Hummingbird suit. While everyone else distracts Kuvira, the Hummingbirds attempt to cut through the mech's armor with plasma torches, but the process takes too long and Kuvira is able to swat them away and disable one of them. It isn't until Korra freezes the mech with a river that they have enough time to cut through. But Kuvira manages to free one of the arms before the cutting is finished, so Hiroshi fires Asami's ejector seat and finishes cutting just before the giant metal hand crushes him. His sacrifice opens a hole in the armor for the others to take the mech down from the inside.
Battle Droid: Do we take prisoners? Hevy: I don't. *BOOM*
The Venture Bros.: General Triester, knowing there's nothing that can be done for him on Earth, decides there's one thing to do: He shoots himself out of a cannon into space, wearing an American Flag as a toga while saluting, and with a note pinned to himself saying, "fix it" to whatever aliens might find him.
Played for Laughs in an episode of Futurama, when Fry gets carried off by a mechanical pteranodon. Subverted in that he lives.
Fry: "This a cool way to diiiiiiee!"
In Superman: The Animated Series, Superman has been beaten by Darkseid and is paraded through Metropolis. Surely, the mere mortals the Last Son of Krypton had defended would gaze upon this and tremble before the might of the ruler of Apokolips, right? Wrong. Dan Turpin stood up to an alien menace that pummeled Superman, and just in time for the New Gods to arrive. But before he leaves, Darkseid reminds the Man of Steel that "every victory has its price", and vaporizes Turpin with a smile on his face.
Superman: (at Turpin's grave) "In the end, the world didn't need a super man. Just a brave one.
Ferro Lad: Long live the Legion... *COSMIC LEVEL BOOM*
Ripcord's sacrifice in the first episode of G.I. Joe: Renegades certainly counts. It was later revealed he survived, but that was long after it seemed his death had become permanent.
Flint Marco AKA Sandman in The Spectacular Spider-Man. He tries to heist an oil tanker, but in the ensuing fight with Spider Man oil starts spilling and then catches fire. Being a decent bloke in heart, Marco helps Spider Man rescue the crew, then throws Spidie himself away from the ship and, as it's about to detonate, forms a protective bubble with his own sand-body around the tanker. The explosion seemingly glassifies him. However, he was revealed to have survived the explosion shortly after Spider Man left. He wasn't seen again in the series. One has to wonder what his role would've been if the series hadn't been cancelled.