Let's see...
I used to give the monsters swords +1, +5 vs. player-characters.
I once gave a single character a helm of brilliance. It was guarded by a few orcs on the first level. Why did I do so? Because that's what I rolled on the treasure tables.
For a while, all my dungeons had DLM's (Dungeon Level Masters). Each was responsible for keeping order in a particular dungeon level, evicting parties that caused too much trouble, restocking monsters, etc. They also served as really lousy plot devices.
We thought the portable hole actually created a hole in something (kind of like passwall). I used a crystal ball and a portable hole to trash so many monster rooms...(scry, see where they are, pop in where they aren't. Rinse and repeat.)
One of my wizards once took out the Egg of Coot (First Fantasy Campaign) by teleporting into his throne room, throwing a bag of holding over his head, then pushing him into a portable hole. Rip in space-time and all that...
We used to run our characters in multiple campaigns, which led to serious balance issues. When I came back from college, I found my friends' characters all had max stats, max psionics, belts of storm giant strength, hammers of the thunderbolts, etc. To challenge them I created the Greek Gods dungeon, where they went from room to room, battling gods, titans, hundred-handed ones, and so on. My favorite encounter was when one wizard tried to use a time stop spell on Chronos (the Titan of Time). BTW, the party trashed the place - no gods survived.
One character had an item that would resurrect him if he died. A drow disintegrated him. A round later he reappeared, sans clothing, equipment, armor - basically starkers. He was the paladin.