Blade of Force( Complete Mage, p. 40)
You can surround a weapon with a short-lived aura of force.
Ability to cast 3rd-level spells,
As long as you have a 3rd-level or higher force spell available to cast, you can surround a melee weapon or a single piece of ammunition with a thin field of force. Activating this ability is a swift action; you must touch the weapon to be affected as part of the action. The next attack made with that weapon, if taken before the end of your next turn, deals an extra 1 point of damage per level of the highest-level force spell you have available to cast. Furthermore, that weapon ignores the miss chance normally granted to an incorporeal creature. If the next attack with that weapon misses, this benefit is lost. As a secondary benefit, you gain a +1 competence bonus to your caster level when casting force spells.