Incorporated into the mechanics of Ace Combat Zero. Sparing noncombatants and wounded, fleeing aircraft earns you respect and means you don't fight the hardest aces (though the ones you do fight certainly aren't slouches), but earns you less money in the long run.
In Army of Two, Tyson Rios makes it a point to try to bring the conspirators within Security and Strategy Corporation to justice, even going to so far as to force Ernest Stockwell, CEO of SSC to turn himself in once they rescued him. His partner, Elliot Salem, who is much more pragmatic and selfish, repeatedly calls him on his honorable nature, pointing out that the two are mercenaries.
Subverted in Bioshock. Though initially Jack is told that the only way to get large amounts of ADAM is to kill and harvest the Little Sisters, Doctor Tenenbaum makes it a point to give Jack gifts for choosing the harder path of rescuing the Little Sisters, by giving him both large amounts of ADAM and unique plasmids. Considering how much more great loot you get from saving them and how little the difference in ADAM between saving and harvesting all the Sisters is (over the course of the whole game), choosing to harvest the little sisters would be a case of Sadism Before Reason. (Or you might do it just to hear the ending where the good doctor calls you out for being a jerk.)
Well, you don't know that you receive gifts when you first start saving them. It could be argued that from a new player's point of view it's played straight initially and by the time you start receiving gifts you've already made your overall moral choice. It only becomes like the above if you already know the full scope of the game mechanic.
In Call of Juarez (especially Bound In Blood), characters will come along and challenge the protagonist to a gunfight, which he accepts. Never mind they have easily pulled a Malcolm Reynolds style move and simply shot them as soon as they showed up instead of doing the whole showdown thing. In the second game they are already outlaws anyway and no one else is around to tell the tale later.
Angeal in Crisis Core, honorable as he is he gave us a warning early on.
Angeal: But I never stole from that tree, because the wealthy man's son was my friend. Zack: If he was a friend, you should've just asked for some. Angeal: Honor can be quite a burden at times.
In the canonical ending of Jedi Knight, Kyle Katarn has Jerec disarmed and on his knees. Jerec tries to goad Kyle into killing him. Kyle responds by giving him his weapon back.
Lupa from Digital Devil Saga is a very strong believer in this philosophy. Tragically, it leads to his downfall because victims of the Atma Virus need to eat their opponents, or they become permanently berserk and have an insatiable bloodlust. Gale then takes up this philosophy after Lupa's death triggers his emotions.
Disgaea 2: If Adell makes you a promise, he will keep it.
Valvatorez takes this to the logical extreme. Want to know why he refuses to drink blood, at the cost of all of his power and prestige: because he promised someone that he wouldn't drink blood until he showed them true terror, and they died before it happened. Not considering death of the recipient a legitimate reason for breaking off a contract, he just went on not drinking blood for the next four hundred years.
More precisely, he learns that while his perfectly logical fighting style is effective, it doesn't allow him to exceed the limits he sets on himself. Only by ignoring reason and logic can he find the power to succeed despite overwhelming odds. He stubbornly refuses to believe that it changes his fighting style, though:
Onion Knight: Don't get me wrong, I still won't fight anyone I can't beat. So I guess I'll just have to beat you!
Alistair in Dragon Age: Origins has a lot of this going on. Being a Grey Warden, he considers it part of his duty.
EVE Online has this in the form of Amarr Empire battle doctrine, which completely forbids retreat or surrender. During their war with the Jove, the only battle they fought with them cost them most of their fleet because they couldn't retreat or give up.
In Fallout 3, with the Broken Steel DLC installed, while the player can send a radiation-immune companion character to activate the purifier rather than sacrificing themselves or Sarah Lyons, the game still considers this a cowardly choice rather than Negating Your Own Sacrifice.
Saber in Fate/stay night and Fate/Zero has a pretty bad case of this. She knows her decisions are going to screw her over yet feels bound by her honor and rules of fair play. As an example in FSN, she charges the temple single handed after everyone agrees it's suicide to do so, is commanded not to go and is perfectly aware that at best she will be severely wounded. In FZ, she lets Lancer go assuming that he's going to kill her Master Kiritsugu and therefore remove her from the war. Why? One, she doesn't like Kiritsugu and two, Lancer just helped her out. He only lives because Lancer lives by the same rules.
Naturally, in Fate/stay night, she ends up the Servant of another person who is the epitome of this trope, Shirou.
Alluded to in Final Fantasy X. According to Auron, Jecht would often try and talk his companions into helping someone out because it was 'the right thing to do.' If he used that phrase, both Auron and Braska knew it would get them into a whole heap of trouble.
Gerik and his mercenaries from Fire Emblem: The Sacred Stones. When they and their employer Prince Innes are vastly outnumbered by an enemy army, Innes tries to convince them to surrender and save themselves since the other guys are only after him. Even after he fires them they refuse to (thoughhe orders them to surrender after firing them).
Innes: Unbelievable... and you people call yourselves mercenaries? I thought you fought for money, not duty. Gerik: Yeah, that's one of the rules. Guess we're lousy mercenaries, eh?
Of course they're still more dangerous than their subordinates because they're ten foot aliens with cloaking devices, energy shields and an one-hit kill weapon. On heroic, which is as close to realistic difficulty, unless if several marines focus fire on the single zealot, he will reach lunging distance before his shields drop and he will annihilate the group of marines by himself.
In the first Kingdom Hearts, Donald Duck briefly follows Riku in his evil phase due to a literal interpretation of King Mickey's orders. He later realizes this is stupid and returns to Sora's side.
In the Kirby series, Meta Knight will give you a sword in the favor of a fair fight, even when the fate of the universe is on the line. In one game, the two of you are on a damaged airship that is currently falling towards the ocean - and he'll wait a full thirty seconds for you to pick up the sword before deciding to attack you anyways. In another, the fact that his evil doppelganger doesn't throw you a sword is the first clue that it's not really him.
Subverted in Mass Effect 2, where Samara, a Warrior Monk swears an Oath to Shepard so she will follow his/her orders, no matter how dishonorable they would be normally considered by her Code. However, she does inform them that if he/she does anything particularly dishonorable in the eyes of the Code, Samara will kill them when she is released from the oath of subsumation.
Played straight and potentially subverted in Mass Effect 3, where Samara attempts to kill herself as her Code requires her to kill her only surviving daughter. However, Shepard can intervene, allowing time for her daughter to provide an alternative.
Inverted with Javik in Mass Effect 3, he chastises Shepard for believing that that victory is possible with one's honor intact.
"Stand in the ashes of a trillion dead souls, and ask the ghosts if honor matters. The silence is your answer."
While several characters from Mega Man X show signs of this, nowhere is it more apparent then in Colonel from X4. By stubbornly refusing to allow his forces to be questioned by the Hunters due to his pride, he is hugely responsible for the Fourth Maverick War, which leaves himself, his sister and the rest of Repliforce dead. In fact, he is one of the few villains from that game who is completely unsympathetic.
Inverted in the Metal Gear series. Being a Stealth-Based Game, Snake isn't averse to using every dirty, underhanded tactic in the book to incapacitate/kill/sneak past his enemies, and Mission Control encourages the player to employ these tactics at every possible occasion, while the villains always announce their presence and proceed to give Snake a (relatively) fair fight instead of just killing him.
Metal Gear Solid 3: Snake Eater: The Boss inverts and plays this trope straight. Her Gambit Roulette ensured that she'd be dishonored and declared "the biggest traitor of this century," her personal honor keeps her from killing, and sometimes even passively helping Snake in his mission. This extends to her Cobra Squad, who were honorable in their fights against Snake despite their abilities, and preserve their honor by killing themselves at the end.
The End is a more pure embodiment, as he wanted "one last" honorable sniper battle. even if he gets the drop on you, he only ever knocks Snake out and drags him to an unlocked cell at a previous base instead of killing Snake. In turn, Snake is sad to disappoint The End if the player lets him die of old age, which causes the Major to chew him out over the radio for trying to be dramatic.
The Fear averts this trope somewhat, in that while he announces himself like the other Cobras, his fighting style is more that of a Combat Pragmatist. He starts the battle by shooting snake with a poisoned arrow, fights in a battlefield littered with traps, and spends most of the battle hiding in treetops with stealth camo. But he also plays it straight, since he doesn't consider poison a fitting death for a warrior of Snake's caliber, and stays around to fight properly rather than let the poison finish him off.
Of course, he still tries to kill you by using Poisoned Crossbow Bolts, and the Game Mechanic's means that you could just heal the poison and be none the worse for wear. He probably just wanted to make sure you were dead.
However, this trope is downplayed when you think about it. If you pay attention, he's actually staring at you while he's bowing, which is considered extremely disrespectful in Japan. He's not so much being honorable as he is being ironic.
In Quest for Glory 2, a fighter faces The Dragon in a climactic swordfight, and quickly disarms him. If he chooses to kill his unarmed foe, instead of letting him have his sword back, the game treats it as a dishonorable act... even though The End of the World as We Know It is due to happen in a few minutes, if the hero doesn't get a move on. The VGA fan remake is even more extreme in this regard; giving the sword back leads to a truly Nintendo Hard fight. Apparently, The Dragon waits until after you show him mercy to bust out the really nasty moves.
In Samurai Warriors, Naoe Kanetsugu embodies this trope to a tee, Azai Nagamasa less so (who splits this with his love of Oichi). Interestingly, the Jerk Ass Ishida Mitsunari actually adopts this trope by his decisive battle at Sekigahara by refusing an officer's suggestion of a sneak attack on the enemy, and revealing in his ending that his friends' honor tropes actually rubbed off on him.
A game mechanic in Sengoku. Honor is gained by such things as donating money to the Emperor and granting land to vassals, and lost by hatching plots and declaring wars. If a character loses too much, they commit seppuku.
Kasumi from Shakkin Shimai takes this to an extreme, refusing help from Okura even if it means she'll be sold into prostitution to pay off her family's debt.
Red from Solatorobo usually acts before he thinks, and, being a generally nice guy, he's usually acing heroically (or stupidly, but sometimes Good Is Dumb). He justification for rushing headlong into a mission that seems hopelessly outmatched is just "I Gave My Word."
Possible in the Star Ruler mod Galactic Armory. One Trait you can take is "Code of Honor", which prevents from using a variety of subsystems. No WMDs, fair enough, but when the thing prevents you from using sensible things like Armor-Piercing Attack it goes straight into this.
Luke, the protagonist of Tales of the Abyss, starts off as being extremely self-centered and arrogant, but later he becomes near-suicidally selfless in an attempt to make up for his previous behavior, and holds true to the strength and ideals of humanity, opposing the fatalist views of the game's antagonists.
The Half-Zatoichi in Team Fortress 2 is a katana wielded by the Demoman and the Soldier. It is Honorbound, meaning that once you draw it, you can't switch to another weapon until you get a kill with it, but getting a kill with it gets you back all your health points.
In the Warcraft book Of Blood and Honor, the human paladin Tirion Fordring is an extremely honourable guy, saving an elderly man from a race which pretty much all of humanity was still recovering from having being nearly crushed by at the time. Doing so saw him exiled for treachery and his wife refusing to take herself and their son into the ruin he made for himself. His magical powers were supposed to have been taken from him, though due to nature of his use of them, it is assumed that they were granted by moral righteousness — which has since been debated and argued about in true nature, due to World of Warcraft.
In Warriors Orochi, Pang De's version of this trope is so cliche that he's called out on this more than once — hilariously, when one asks him what his "way of the warrior" even means, Pang De's explanation is basically repeating the concept. It's especially off, and call-out-on-worthy, since he's on Orochi's side through Wei, particularly Cao Pi's aligning with Orochi. However, in the Battle of Shizugatake (Shu story) if the player manages to save enough Hojo officers and prevent defections he will recognize the conflict and agree to leave Wei/Orochi.
In a rare villainous example of this trope, in Weaponlord, it has been prophecied that on the night that the moon bleeds, the Big Bad Zarak will be killed by the Weaponlord, whose identity is unknown except for the clue that he/she was born under the Warrior's Moon. Zarak's lieutenants advise him to pull a Herod and simply slaughter all the infants born under that moon, but Zarak instead decides to wait until the Weaponlord is grown up, and then face his prophecied killer fair-and-square in single combat to see if the prophecy will really work. This gets Zarak killed if you play anyone but him, and if you play Zarak himself, it is revealed that Zarak himself was born under a Warrior's Moon, and since he killed the previousBig Bad, Zarak himself becomes the Weaponlord.
The White Knights of RuneScape apparently value the honour of a straight-up battle that would leave many of their number dead over the reasonable approach of sniping the enemy leader from above and behind, almost expelling the member of their order that took the latter approach to killing a dark magic-wielding enemy warlord.
The Arceans in Galactic Civilizations are all about honor, even at their own expense. This why, despite being generally nice enough guys to those who aren't their enemies, they are considered morally Neutral: honor is more important to them than any morality. A savvy player can exploit this to get the Arcean AI to do some very stupid things if they set things up properly.