Luck and antimagic talismans are also good, inexpensive uses of an empty misc slot. Depends on the expected threat and existing strengths of the unit.
Hell Sword is fun; like the Wraith Sword it's 2-HD, but in addition to life drain it gives berserk and fire resistance. Plus, for devils of the flaming variety it's more thematic, although they admittedly don't benefit much from the fire resistance bonus.
