The Reciprocity Coin was my submission for RPG Superstar 2011. The basic concept is a coin that can be activated when given in a transaction - the giver then gets to make a demand of the receiver, and then the receiver gets to make a demand of the giver.
It's an unusual item, in my eyes, because it's built as kind of a player-owned plot generator. And because reciprocity and carefully crafting intricate demand phrasings are fun :)
So I'm reasonably pleased with the item itself, and I got a lot of interesting feedback for it, collected here, mostly for my own future reference.