Arms and Equipment Guide has Ghostoil. 50gp, full-round action to apply, allows your weapon to affect incorporeal creatures normally for two rounds.
Complete Adventurer has Ghostblight. 100gp, standard action to apply (swift action if you have a weapon capsule retainer), allows your weapon to affect incorporeal creatures normally for three rounds.
Spell Compendium has the Ghost Touch Weapon spell. Cleric 3, so Oil of Ghost Touch Weapon would cost 750gp and last 5 minutes.