Ghost Touch Weapon

(Spell Compendium, page 102, DnD 3.5)

Transmutation

Level: ; Cleric 3
Components: V, S
Casting Time: 1 standard action
Range: Close (25 ft. + 5 ft. / 2 levels)
Target: One weapon or fifty projectiles (all of which must be in contact with each other at the time of casting
Duration: 1 minute / level
Saving Throw: Will negates (harmless, object)
Spell Resistance: Yes (harmless, object)

With a few words and a gesture, you empower a weapon to strike true against incorporeal foes.

Ghost touch weapon makes a weapon magically capable of dealing damage normally to incorporeal creatures, regardless of its enhancement bonus. (An incorporeal creature's 50% chance to avoid damage does not apply to attacks made with weapons under the effect of this spell.) A ranged weapon affected by this spell does not bestow the ability on its ammunition.
The weapon can be picked up and moved by an incorporeal creature at any time. A manifesting ghost can wield the weapon against corporeal foes. Essentially, a weapon under the effect of this spell counts as either corporeal or incorporeal at any given time, whichever is more beneficial to the wielder.