In Dan Abnett's Warhammer 40,000Gaunt's Ghosts novel His Last Command, when Gaunt and his team are brought before a tribunal on suspicion of being Chaos-tainted, Ludd volunteers to defend them. Although he is a junior commissiar, he knows no one else will and that they will assigned someone who hates them if he doesn't.
In Blood Pact, when Dalin Criid delivers a report, Hark knows there's another reason because it doesn't take two and he can see Merrt in the hall behind him. Merrt tells Hark that he came for moral support.
In William King's Warhammer 40,000: Space Wolf novel Wolfblade, while Ragnar awaits his Trial of the Mystical Jury, his friend Sven stays with him, grousing about the injustice, until their old teacher Ranek comes to send him away, saying his loyalty does him credit but might harm him. Then Ranek explains that he will defend Ragnar, that he volunteered to do so, and that he believes he is not Chaos-tainted.
At the end of Sandy Mitchell's Ciaphas Cain novel The Traitor's Hand, when Cain is awaiting the judgment of the tribunal, the colonel and XO of his regiment wait with him.
In Galaxy in Flames, Tarvitz realizes that the ship following him is under the command of a friend, Garro, and appeals to him, telling him of Horus's treacherous attack. Garro shoots down his pursuers, and then begs him to assure him that he told the truth.
In Betrayer, when Angron is buried under dozens of meters of rubble, Lorgar teleports there and starts to dig him out despite being under heavy attack, thus beginning the two's Odd Friendship.
In Scars, Leman tries to invoke it on Jaghatai when under Alpha Legion's attack, but by this point, the Khan doesn't know who's loyal and who's a traitor and all but ignores him in favour of going to Prospero to find out.
Also in Scars, Jaghatai promises Horus that he'll always help him, but ends up breaking that promise when Horus goes traitor.
In C. S. Lewis's The Horse and His Boy, when Shasta tells the horse that he really needs someone who could tell him whether the nobleman is evil, Bree reveals his speech to tell him that he is. Which gives Bree the opening to suggest that they could run away together.
Later, when they meet Aravis and Hwin, Aravis reveals that Hwin stopped her from killing herself before their decision to run away together.
In Death Masks, when Harry needs a second, Charity, although she despises him, truthfully says that Michael would have helped him, and Shiro volunteers to fill the role. Later, Shiro voluntarily takes Harry's place as Nicomedus's prisoner.
In Dead Beat, Harry hears Billy and Georgia talking: Billy wants to help Harry, but Georgia is afraid that his trouble is too big for them, and so they would end up hindering him instead.
And in Proven Guilty, Murphy comes along to help him pull a Big Damn Heroes moment even though she's in the middle of leading an investigation and got demoted from head of SI to sergeant for disappearing.
As of Changes his friends all show up to help him when he needs it. Not all of them make it out, and Murphy at best is getting a half pay retirement.
Ghost Story shows that there were further consequences. Molly's injury left her with a limp, and she's not all there, thanks to being a sensitive who went into battle, surrounded by the psychic effects of death and black magic, not to mention the bloodline curse.
In Cold Days every single one of his allies spends at least a few minutes chewing him out, using varying degrees of subtlety, for thinking they would abandon him just because he became the Winter Knight.
In Skin Game has a domino effect of this.
Now retired paladin Michael Carpenter sees Harry and Karrin about to be killed in front of his lawn, and despite his crippling injury, offers to come out if Nicodemus would stop his attack. Harry and and Karrin plead to him to not do this, but he does so because they are friends.
During the same scene, he openly calls Archangel Uriel his friend. Uriel is bound by many Laws that keep him from messing with freewill and people's choices. What Uriel can do is help Michael in fulfilling a Choice Michael has already made and loans Michael his literal Grace of God, restoring Michael to full health. And if Michael abuses this Power while holding it, it will cause Uriel to Fall.
Because of the above scenes, Waldo Butters is helping protect Michael's home and when Harry goes down and Charity held by Nicodemus' crew, to be forced to watch as Nicodemus burns the house down with all her children and friends inside. Butters makes a choice to sacrifice himself not to stop them completely, just buy time until other help can get there. His faith in Right overcoming Wrong combined with the other acts of Faith Harry and others make that night, allows for a Divine Aide to appear and sends Nicodemus fleeing.
In Gaudy Night, after Harriet has defended his detecting — even if he does it for fun, he does do it, and many people have reason to thank him — and another woman brings up a neighbor who had helped with her drains for nothing because he liked working with them.
Ron and Hermione in Harry Potter, who repeatedly risk their lives out of loyalty to Harry when they could easily choose to go about their normal teenaged lives instead. In Ron's case, he's willing to make a Heroic Sacrifice on Harry's behalf as early as the first book.
The Marauders (Harry's father and his best friends) all support their friend Lupin instead of spurning him when they find out about his furry little problem (he's a werewolf).
Marietta is apparently the only member of Cho's posse to stick with her after she became distraught over Cedric's death and started behaving differently in her depression in Harry Potter and the Order of the Phoenix. Unfortunately Cho pushed this too far and forced Marietta to join the DA when she wasn't comfortable with it and didn't take the group seriously resulting in her betraying them in a move that almost got them all expelled, Cho included, and caused problems for the many of their relatives who were employed by the ministry. Fudge coming to expel Harry with Aurors along implied he wanted to toss him in Azkaban for starting the group. The only reason it didn't ruin or seriously hamper her fellow students job prospects is because Dumbledore intervened.
In Nick Kyme's Warhammer 40,000 novel Salamanders, Daki'er, when troubled by his discovery of an artifact, appeals to Ba'ken to forget that he is his sergeant and speak to him as his friend; Ba'ken tells him that it does seem that he was intended to find it and touches his arm in support.
In Edgar Rice Burroughs's The Gods of Mars, when Xador loses favor because of his defeat at John Carter's hands, all his erstwhile friends fail this utterly, much to Carter's horror. Carter therefore intervenes on his behalf.
My blood was up. For minutes it had been boiling at the cowardly treatment they had been according this once powerful comrade because he had fallen from the favour of Issus. I had no love for Xodar, but I cannot stand the sight of cowardly injustice and persecution without seeing red as through a haze of bloody mist, and doing things on the impulse of the moment that I presume I never should do after mature deliberation.
Later, when a companion proposes a way to escape, John Carter says he can't leave Xodar, and his companion agrees that recapture would be better than deserting a comrade.
Still later, Kantos Kan, Carter's Fire-Forged Friends from A Princess Of Mars, pledges his support to Carter after hearing a death sentence on him. Fortunately, this inspires the crowds.
In The Chessman of Mars, when Tara is on trial as a Corphal, U-Thor advises her:
"Yet you do not deny the accusation," said O-Tar. "It is not worthy the dignity of a denial," she responded haughtily. "And I were you, woman," said a deep voice at her side, "I should, nevertheless, deny it." Tara of Helium turned to see the eyes of U-Thor, the great jed of Manatos, upon her. Brave eyes they were, but neither cold nor cruel. O-Tar rapped impatiently upon the arm of his throne. "U-Thor forgets," he cried, "that O-Tar is the jeddak." "U-Thor remembers," replied the jed of Manatos, "that the laws of Manator permit any who may be accused to have advice and counsel before their judge."
In A Fighting Man of Mars, when Tan Hadron has been condemned to The Death, his fellow prisoner Nur An condoles with him and tells him they will suffer together. Tan Hadron encourages him, reminding him they aren't dead yet.
In Terry Pratchett's Unseen Academicals, Glenda and Trev both stick up for Nutt. Trev, in fact, tells Ridcully that Nutt is his friend, and he won't stand for him being hurt.
Christopher Robin pretends to believe that Pooh is a cloud to try to fool the bees and shoots down the balloon to get Pooh away from the bees.
Christopher Robin reads to Pooh when he's stuck in Rabbit's front door.
Pooh and Christopher Robin go to rescue Piglet in the flood, and Owl, well-intentioned, goes to encourage him with news that rescue is coming and tell him a story to divert his attention (accidentally endangering as it nearly puts Piglet to sleep and causes him to slip into the flood, but he meant well).
Pooh helps Tigger find something to eat.
Tigger goes to rescue Rabbit when he's lost in the mist.
Piglet volunteers his home for Owl to live in after Owl's is destroyed.
Pooh says Piglet would come live with him if he lost his home.
In Charles Dickens's A Tale of Two Cities, Charles Darnay returns to France to save the man who had adminstered his estates while he lived in England; and, of course, Sydney Carton.
In Wen Spencer's Endless Blue, Mikhail recalls such moments between him and Turk: Turk's stopping him from committing suicide, and his attacking a man who had hurt Turk, because Turk had bitten the man, and by attacking, he ensured that this was not just a matter of a Red attacking a human.
In Roll of Thunder Hear My Cry, David Logan sacrifices the cotton crop by setting it on fire, to distract the lynch mob from going after TJ. The cotton crop was the only thing generating income for the family at the time. His wife had lost her teaching job (at the fault of TJ), he was unable to return to his railway job because of an injury. Also, this takes place in the 30's.
Also, Hammer, David Logan's brother, who lived and worked in the North, had previously been shown to making enough money to buy a Packard car, the same type as a wealthy white family in the area possess. When he receives word about his family's financial difficulties and the immediate need to pay the mortgage (courtesy of a particularly nasty white who wanted the land), he sells the car for the necessary money.
In Kenneth Grahame's The Wind in the Willows, Badger, Rattie and Mole set out to prevent Toad's insane obsession with cars from ruining him. He escapes their attention by convincing Mole that he needs a doctor. Later, they help him reclaim Toad Hall.
Hermes offers to Amelia to assist them. They wisely do not trust him but have to get his help.
Romus helps against Mrs Wren and leaves Amelia and Quentin with gifts.
Miss Daw can not fail to warn Boggins if they try to escape, but she does overlook everything that is not an escape attempt, and dallies when she must tell him. At her request, Corus also lets Amelia escape.
The ship picks them up in the middle of the sea. Victor weighs whether to help the ship even at the price of risking the universe because of this assistance; Colin refuses to not help. And when Amelia goes off to save them all, Vanity and Colin come after her.
In Terry Pratchett's Only You Can Save Mankind, when Johnny realizes Bigmac has seen his friends crash the car they stole, he is running after him before he even thinks; he stops Bigmac from getting too close.
In L. Jagi Lamplighter's Prospero's Daughter, Astreus toward Mephisto, though it takes Miranda a while to figure out how, and then how badly he paid for it.
In Prospero Regained, the siblings are always having to rescue each other. And come through.
In P. G. Wodehouse's Hot Water, Packy sets out to help Jane and Blair Eggleston out of fellow feeling another pair of lovers. Later, Soup Slattery does something because among his few principles is to never let down a pal.
This is also how, in the Jeeves and Wooster stories, Gussie met Madeline: she went for a walk, and he helped her with a thorn.
In Teresa Frohock's Miserere: An Autumn Tale, Lucian quickly goes to help Lindsey when he realizes she needs it, without having met her first.
In Devon Monk's Dead Iron, when Rose is thrown out of the meeting where the Witch Hunt is started, she resolves that nothing can stop her from helping Mae.
In Gene Stratton-Porter's Michael O'Halloran, Douglas, in the opening, intervenes when Mickey is about to fight a boy twice his size for cheating him, and makes the other boy cough up the money. Shortly thereafter, Mickey takes in the crippled girl Peaches to prevent her going to the Orphanage of Fear.
In Devon Monk's Magic to the Bone, Zayvion does this, repeatedly, for Allie, such as giving her money for a taxi. She is suspicious of motives, though his working for her father does give her some reason.
In John Hemry's Paul Sinclair series, most of the junior officers will stick together, as when they attend Wakeman's trial to provide moral support during Sinclair's testimony.
In Poul Anderson's "A World Called Maanerek", Smit thinks he is being this when he suggests that Wanen could watch a woman being lobotomized, have the first chance to rape her, and then throw her out the airlock when she was used up — "tension release" as the Hegemony puts it. Wanen feels an "illogical resentment" for it, and then realizes that he's insane.
In P. G. Wodehouse's Jill The Reckless, Freddie thinks he is being this when he goes to the train station where Derek is meeting his mother.
In Robin McKinley's Sunshine, many people from the coffeehouse help out Sunshine after the kidnapping. Constantine also helps cure her; when Yolanda confirms that he had done so, she is willing to take it as proof of his friendliness, even though he's a vampire.
In Beowulf, Wiglaf goes to help Beowulf against the dragon.
Winds up being serious subverted in A Song of Ice and Fire with Tyrion and Bronn. Bronn made a point of warning Tyrion just after they met that he was interested in money, not in risking his neck for no benefit to himself. Three books later, when they've become close — Bronn saving Tyrion's life several times, Tyrion using his influence to get Bronn more wealth and power than he could have ever dreamed of — Tyrion finds himself in desperate need of a champion to help prove his innocence in a trial that is rigged against him. Bronn winds up turning him down, reminding him that he did, in fact, make the nature of their relationship clear right up front. Tyrion has to settle for A Brother In Need instead.
In Captain Vorpatril's Alliance by Lois McMaster Bujold, Ivan to Tej and Rish — sheltering them in his apartment and then staging a fake marriage to protect them. The consequences for him snowball. When they are trapped underground, Tej is glad she can be there for him because their situation brings back painful memories for him.
In Andre Norton's The Zero Stone, Eet saves Jern and the captive patrolman from the Guild; he points out to the Patrolman that he was lucky that Eet and Jern have an alliance, since he had to rescue both of them.
Thinner: When his wife fails to believe he is cursed (and in fact conspires with a local doctor to commit him to a Mental Institution should he return home), Billy turns to Richie Ginelli, a Mafioso who he is acquainted with. Richie sends Billy a doctor, then shows up himself to wreak havoc on the Gypsies until they agree to lift the curse. He dies for his troubles, but accepted that fact beforehand.
Les MisÚrables: Grantaire can't do anything to prevent Enjolras from getting shot by the Army, but he can stand by him so that he doesn't have to die alone.
In Mark of the Dragon, Homeless Mayor Mike Jones lets Rosario and Arkay hide in the homeless camp and sleep in his tent when they're running from a Necromancer, despite the fact that they got thrown out previously because of Arkay's anger issues.
Rosario found a starving, deathly ill dragon and spent every last penny she had to nurse it back to health. Now it's her BFF and bodyguard.
Towards the end of Gauntlgrym from The Neverwinter Saga Jarlaxle of all people jumps into the maw of an erupting volcano to rescue Arthogate. This would have been a Heroic Sacrifice if not for him being crafty enough to save both of their skins in the last moment.
Being too willing to do this is Percy's fatal flaw in the Percy Jackson and the Olympians series (and all subsequent series where he appears). It comes to the point where Percy is more inclined to choose his friends in any conflict, even if letting them die would mean saving the world (such as when he hurls himself into Tartarus to save Annabeth).