Amulet of reflection

This amulet grants the intrinsic Reflective, which causes many magical rays to bounce off the wearer. Besides the obvious defensive use, reflection has a fair bit of offensive potential -- the classic trick is to get a monster between you and a wall, then fire a wand or suitable spell for multiple damage as it bounces back and forth. This turns even a mere Magic Missile into a real killer, as at high levels its range can be quite long -- and that means many passes for the victim.

Unfortunately, not all spells and rays bounce -- notable nuisances include Poison Bolt, Frost Bolt, and most dragon breath (though a Blue Dragon's lightning does bounce). It also does not protect against explosions or missile weapons, nor from any wand or spell which does not produce a ray.