Kid Radd: Bogey lets the titular character kill him in the final chapter, dropping a power-up that saves his life from an imminent, apocalyptic blast. It's very effective.He gets better though.
In El Goonish Shive, Nanase experiences the pain of death repeatedly (through the repeated destruction of her fairy-doll avatar) during her fight with Abraham for Ellen's life. She has to be hospitalized afterward due to the extreme expenditure of magic and loses her magic completely for over 2 months.
It also earns him incredible respect from the Jagermonsters. Maxim even gives up his hat (the one thing Jagers prize above all else) to be buried with Lars, because he's made himself as good as a Jager with his act, and no Jager should be buried without a hat. Maxim walks hatless from that point on, until he acquires the replacement in a suitably epic mini-arc.
Erfworld: Bogroll taking down Lord Ansom himself. There's no possible greater glory for the lovable oaf.
Fleep. After discovering a very nasty truth about his past actions, Jimmy gives up his chance of being rescued in order to assure that another civilian would survive. Jimmy's own internal monologue downplays the heroism of the sacrifice—he just wants to see his wife, and now that she's dead, redemption is the only shot he has at ever seeing her again.
Mob Ties: Mika was very nearly killed by Bengal, but for Kyoko, the Love FreakGenki Girl, leaping in front of the knife that would have killed her.
Mika: "You idiot! Why did you hurt yourself to protect me?"
Kyoko: "Because it's your wedding day, silly! You should be happy on your wedding d..."
Mika: "Kyoko? KYOKOOOO!!!"
In Roomies, Ruth dies stopping a drunken Danny from driving into a truck.
General Tagon (Captain Tagon's father) comes at this from a strategic angle. If you're going to sacrifice someone, it should be someone you care for—if its someone you hate, its not a sacrifice, its murder. This ends about as you'd expect.
Captain Kevyn: You have many friends, general?
General Tagon: Alive? No, not really.
Homestuck: Jade sacrifices her Dream Self to push John out of the way of an oncoming meteor in the End of Act 4.
Another one happens in Act 5, "Hivebent", when Sollux withstands the Mind Rape of an Eldritch Abomination's cry just long enough to get Feferi into the Medium.
Feferi allows her dream self to get killed so she can prove the Horrorterrors of the Furthest Ring aren't at all something to be feared, so she can interact with Jade on a more personal level.
Sollux has another go at it when he overexerts his powers to propel the asteroid to the green sun before their window of opportunity passes.
During the Escape from Brassmoon story arc of Goblins, a group of monsters is holding off guards by the gate while waiting for it to open. It finally does, to their relief and joy, only for a group of guards to charge towards them. The ogre in the group pushes the others towards the exit, grabs a spear and goes to meet the guards. Two pages later, you see two of the guards stabbing him repeatedly.
Subverted in the same arc a few pages later. Complains tells Big Ears that he's badly injured and can't move, so Big Ears will have to—and Big Ears cuts him off, furiously telling him he won't leave him behind. Complains stares at him for a moment, then:
Are you high?! I was going to say you should find a board or something to put me on, and you could maybe drag me out of here! Damn right you're not leaving me behind!
Played with in the case of Chief, who stayed behind to fight Kore to allow the rest of his group a chance to escape and hide in a dungeon crawl. The other goblins decide to go back to save him after they hear his screams of pain, but they utterly fail to do so.
In Powerpuff Girls Doujinshi, Atomic Betty was about to get crushed by a giant robot claw (they never showed the robot), then Sparky runs and pushes her out of the way so he could get crushed to death instead. Leaving Betty with a big Say My Name.
Tales of Gnosis College: Moira makes one in hopes of preserving friendly relations between humanity and Howard the Tentacle Beast's species. Nanetta makes one for Moira at the same time.
In the "Futures Trading" story arc of Dr. McNinja, Chuck Goodrich was protected from far by the NASAGhast, which killed any of the dinosaurs that tried to harm him. But the battle was being lost due to the dinosaurs' ultimate weapon, the Horrorsaurus. In a moment of honor and courage, Chuck provoked the Horrorsaurus into attacking him so the NASAGhast would kill it, but the spirit didn't act quickly enough to prevent his gruesome death.
