Excerpt from Bheind the Vault Door: Unique Items
Many GM's have a difficult time maintaining the feeling of excitement and prestige and power that magic items should create. It's not hard to understand why though. Beyond the lowest levels; magic items are ubiquitous and any spellcaster, and many no casters can learn to craft them. But the simple solution then, is to change this dynamic. Consider this variant in which there is only one of any given permanent magic item in existence. No magic items can be created and instead they are forged in the fires of legend and battle. Every magic item has a story of its creation and abilities unique to itself. Buying an item is difficult as they are immensely rare and expensive, so only the finest of shops have them available. There is only Holy Avenger, one Bracers of armor+6, one cloak of resistance+3, one Vorpal sword, and so on.
This has a number of effects on game play. First of all it means someone can be easily recognized by their item. A knight who wields "THE Holy Avenger", is far more memorable than a knight who wields a holy avenger. It also means that if a player wants or needs a specific item there is only one way they can get it. Instead of buying it from a store or having a caster make one they must venture to where it is and acquire it. Going after a particular item becomes its own adventure hook. Additionally, this change adds extra value to any class feature that allows one to add enchantment to their hands or a weapon, giving them the chance to customize a weapon with magical abilities in combinations that may not exist anywhere.
This also means that magical items that previously seemed mundane or boring become unique and in demand. If every barbarian hero can have a mug of endless mead then it's nothing more than a meaningless trinket. But if there is only one, just imagine the hordes of heroes and drunkards who would be perusing it. It also means that while players can still buy some magic items, they're limited to just what the GM decides is in stock, and each purchase is something truly special. Overall this rule causes players to have very slightly lower statistics, depending on what items they get a hold of, but they will still have access to the items they need to overcome challenges. This leads to players buying and finding and using much less common, but more interesting, magic items and having to get creative with using them to their best effect. This simple change can help restore the glamour and glory of magic items, making them rare and powerful once again with minimal effort.
The only extra work this requires is for the GM to make a note when a magic item, or magic armor or weapon quality appears in setting. If the players slay a dragon and find the boots of striding and springing, the GM writes that down on a master item list and then doesn't use those boots anywhere else. From there a proactive GM can also think ahead about some items and where in the world they are, using them as pieces of world building and as handy adventure hooks. Challenge rating, the cost to buy magic items, and random loot don't need to be adjusted at all, apart from random magic items not including ones that have already been planned or used.