First, I love the physics defying ones: Portable Hole and Rod of Inertia (Immovable Rod in later editions).
Second, I love items with quirks. Not just a +1 Sword, but a Sword +1, +4 Versus Reptiles! Forgotten Realms had loads of these.
Third, Ioun Stones and Figurines of Wonderous Power.
Fourth, Ridicuously Powerful Rings of Blowing Things Up (or Ring of Shooting Stars and Ring of Elemental Power as they were officially called).
Fifth, and much missed, Potions of Doing Stuff Spells Couldn't Do. Gaseous Form, Treasure Finding, Oil of Slipperiness amongst others.