Moonlight shone bluely off the great blade which lay waiting. "In this sword is locked that before which they (the evil hordes) cannot stand. When their demon gods have been driven back into the Middle World, the human savages will despair and flee. We got here soon enough."
He looked up at the figure on the cross. Bending, he took the sword Cortana in his hand… Holger felt the illusion that masked him dissolve. And his memory returned, and he knew himself.
-Poul Anderson, Three Hearts and Three Lions
Folks often comment how much inspiration Gygax took from this book of Anderson's; they say Holger Danske, Ogier the Dane, is a model for the paladin class, and he indeed performs many classic paladin deeds - detecting evil, laying of hands, bonded with an intelligent war horse. The D&D troll is clearly from this book, and the story explicitly uses the Law vs Chaos alignment axis. When the civilized realms of man are identified as bastions of Law, I hear echoes of Keep on the Borderlands.
But an overlooked piece at the end is when Holger finds the object of his quest, the magical sword Cortana, buried in a ruined Christian chapel in the pagan lands. All the forces of Chaos in the story have contrived to keep him from finding this powerful weapon, for it is said it can singlehandedly turn back the tide of Chaos.
I highly recommend checking out Three Hearts and Three Lions if you're a student of D&D's history; it's one of the stronger inspirational sources. I have a review of it here: Three Hearts and Three Lions review.
Changing gears, I wonder how many folks have used an actual holy sword in their game? I can't recall too many instances of such a weapon showing up in the published works - the one that stands out for me was an Astral jaunt published in Dragon, where the party travels to recover the holy sword "Fedifensor", defender of the faith, and battles githyanki.
I'm confronted by the question of when/whether to introduce any holy weapons, as my regular campaign (on hiatus due to the holidays) will resume with the characters in the mid-levels - levels 6-7 - about to embark on their world shaking quest to recover the Demonomicon. And they have a paladin as a main character. Sooner or later, the question will arise regarding the possibility of finding or using such a powerful item to aid them.
Would a holy sword be strongly tied to a deity or particular religion? Meaning a Holy Sword dedicated to St Cuthbert wouldn't work fully for another Lawful Good deity, if the setting were polytheistic? Perhaps that's getting too close to the uncomfortable question of whether scrolls of clerical magic in the possession of an evil cleric are dedicated to the evil deity in some way, and couldn't be used by the lawful cleric that claimed them. There seems to be a strong need for such items to be fungible and usable regardless of religion.
It's given me the chance to consider how such a weapon would exist in the setting. Any holy sword previously created or recovered by servants of the main religion would quickly find their way into the hands of the established hierarchy, and would be heavily guarded and kept at a central location. The questing knight that first recovered such a weapon, assuming he's not the church's champion, would likely be instructed turn it over to the Patriarch or similar leader; we're talking about pious lawfully aligned characters, after all. It's unlikely such a powerful deterrent would be sent out into the world on missions, unless it were in the hands of the religion's established champion. The risk of loss is too great. Our paladin in the campaign is from an ancient sect that predates the primary monotheistic church, so it's even more unlikely he'd be able to gain the confidence of the theocracy.
Holy swords still lost would be just that - lost and forgotten - or heavily guarded by minions of evil or the forces of chaos, to prevent their recovery. In the excerpt of Three Hearts and Three Lions, there was an arduous quest into the pagan lands, a vicious fight against a troll, and the forlorn cemetery around the church was guarded by the "Hell Horse", a minion of Hell itself.
For Gothic Greyhawk, such a weapon is in the hands of the Church of the Blinding Light, the theocracy behind the Pale. It's unlikely players would ever have access to an existing holy sword in a meaningful way. Rather, the players would need to make it an explicit goal to determine if such a weapon were ever lost in a previous age, and make it their primary quest to recover if it themselves. And even then, they'd run the risk of the bureaucracy stepping in and laying a claim to the weapon in the name of the greater good.
I could always go the Excalibur route, and have such a weapon come from "on high" for a limited purpose, returning to the divine realm or the great beyond once it's limited purpose was fulfilled. I need to think on it further; having the sky break open and an angelic being descend to earth on a shaft of golden sunlight is completely over the top, but could work in a game where the cosmic strife between Law and Chaos boils in the background.