Fire and Frost Brand
Fire and Frost Brand are two very similar weapons. They are both unaligned artifacts, both do d5 to hit and double damage against a set of monsters, and both convey the appropriate resistance. However, Frost Brand is vastly more valued than is Fire Brand. Frosty does more damage to beings which are NOT cold-resistant, while Fire Brand hits those without fire resistance, a group which includes most of the demons and some other big nasties. One notable thing, though, is that most of the creatures seen in Gehennom are not fire-resistant, and neither are the monsters on the astral plane. Fire brand is very undervalued.