A sword that stores the identity of the wielder. To transfuse the soul to the blade, one must first stab himself through the heart. The person will not die, but lose the freedom of the soul upon real death.
A Cloak of Shadows that causes mushrooms to grow in its own shadow. A crouching theif might find himself in a ring of poisonous toadstools, an interesting thing for a sentry to find after the thief has left hiding place.