Sphere of Annihilation. How cool would it be to have your own miniature, gravityless, telekinetically controlled black hole? It would make my commute a LOT easier. Also great for garbage disposal, hiding of corpses, and other such endeavours.
If I could get a second item, I'd go with a Talisman of the Sphere. I really wouldn't want that thing coming back at me!
Hmm. I think I go for a Ring of 3 Wishes, wish only a single, special wish I am not willing (and perhaps not able to explain well enough in English) to write down here, and than give the Ring to someone else. I only need a single wish.
Necklace of Adaptation..... can you say astronaut or exploring the ocean? chemical warfare necklace etc.... give one of these to every child and no more drownings....