Here's another specific example, which I guess you'd file under either "placate", or else "sacrifices self to uphold one's honour".
Ok, I love hearing campaign stories and this one is great. However, I'm not sure I get it entirely...you agreed to surrender and attend a "fair" trial and you also agreed to your mount being spared if you did not use it to escape. I presume you were already completely breaking the agreement to begin with by attempting to escape and circumvent the "fair" trial. Why jump off the mount and just to honor that part of the deal?
At any rate, IMC I wouldn't hold it against a paladin for attempting to escape what he reasonably thought was a bogus trial overseen by evil creatures - but I see your point here.
The more I think about this, the more I come to the conclusion that while such an ending can work well for a novel or a movie, it's not a good thing for an RPG. So the second part of the point of the thread is: how can heroic sacrifices be presented by the DM such that there is no bitterness from the players or having the heroism fall flat?
I think several of us have touched on that but it was lost in the tangent. The way to do it is to make it more of a player dependent choice and to make an engaging campaign world which they care about. In the examples I gave, I never set out at the beginning of the campaign to require a sacrifice it just sort of naturally evolved out of the game and story. If it works and your players care enough to do it, it will happen.
Now, I can't say I would rule out starting a campaign like that. It could be fun - some vague prophecy about a party member sacrificing themselves. It could provide some dramatic tension if played right. People would wonder from session to session who it might be and you know, a sacrifice situation may even organically develop just by you planting the seed.
Or -if you're a good storyteller - your players can just think the said sacrifice organically happened while you conspired all along. Yes it's borderline "rail roading" but I've had a few times in my games where players deep into the campaign start pulling together all the threads (I go pretty complex on plotlines) and start to see how their characters have fulfilled some kind of prophecy "inadvertently". The players have then asked "how did you know?" rather incredulously. I mean is it truly railroading if the players all happily bought the ticket and piled on?

Most times, I try to build the big themes arond my PCs anyway, so its a custom made "Railroad" if such a thing ever happens in my games.
[sblock= Eyru Story Time]
As an example, I once had a player playing the cleric of a long forgotten goddess of Battle. The Battle Crow, Maeve. As her sole representative, he began to be seen as something of a prophet. A great war between humans and the Giants was brewing and it was on a scale not seen for 500 years. So his rise to power (through traditional levels etc) was occurring simultaneously as this great foe was awakening from it's slumber.
There was growing "prophesy" that the herald of Maeve was soon to come and with it a terrible war. The cleric himself had been told such prophecy and began having visions of his goddess and fields of battle covered thick in ravens.
Well, it just so happened that a fight went terribly wrong during the campaign and I had little control over it. A Nightwing (something the party should have left alone) had confused the Barbarian as it arose to defend and evil temple the group was defiling. The fight was already going poorly and when the Barbarian rolled to "attack nearest" the Cleric was right there on hand naturally. The barbarian then, naturally, crits the Cleric nearly felling him with a single blow from his lightning infused greataxe.
At this point, the party was already trying to escape, so the plan was to teleport people out. They had no way to remove the Barbarian's confusion, so the cleric healed himself and grabbed hold of the Barbarian as he wander aimlessly the next round - someone had to do it and he stepped up. The Wizard grabbed them both and they teleported the group to the Sorcerer's "adventuerers college" (note to self: never let a sorcerer take Leadership...)
One problem - the Barbarian was still confused. The sorcerer runs off to find a someone from her entourage that can remove this spell. The Wizard gets the HECK out of dodge (might have been a Dimension Door even). This leaves the cleric who, looking aorund seeing a gathering crowd of "adventurer trainees" stands firm. Cause, he just healed himself and he can "take another hit" if he needs to.
Barbarian rolls "attack nearest" again. Luckily, it's the similarly leveled Cleric and not a hapless follower, everyoe agrees. Cleric shrugs, he'll make it. Barbarian CRITS THE CLERIC AGAIN. Drops him stone dead.
That night, the herald of Maeve was born. The cleric became an NPC, however I don't think he was disappointed as his PC was immortalized in a very interesting story wise and play wise manner.[/sblock]