Along with coming up with some really cool magic items, our DM likes to make magic items that are cool but have pretty nasty drawbacks or are just plain wierd.
Case in point:
Ring of Bone – A ring crafted from the bone of a devil. Crafted by the late necromancer, Dokrikus, for the general of his army. The ring allows the wielder to expend a charge to mold bones into armor. The AC of the armor is equal to the HD of the creature it came from, not to exceed 15. The armor lasts for 10 rounds before another charge must be expended to keep the armor. Additional charges may be used to add bones to the armor, but charges must be spent per corpse to maintain it. The ring holds 30 charges and can be recharged, but only the late necromancer knew how (he did this to keep the generals reporting to him). The ring is currently out of charges. The last ability of the ring uses no charges but can pull the wearer’s own skeleton from his body to act as an exoskeleton, the armor bonus for this method is a d6 + ½ your level. The transformation is painful and deals 1 pt of damage per round that the armor is up, and spell casting requires a concentration check.
We have carried this item around for 17 levels and no one has yet to use it. Literally, on the first charge, your bones come out of your body and form an exoskeleton of sorts.