You can channel arcane energy into your melee attacks.
Prerequisites: Ability to cast 3rd-level arcane spells, base attack bonus +4.
Benefit: When you activate this feat (a free action that does not provoke an attack of opportunity), you can channel arcane energy into a melee weapon, your unarmed strike, or natural weapons. You must sacrifice one of your spells for the day (of 1st level or higher) to do this, but you gain a bonus on all your attack rolls for 1 round equal to the level of the spell sacrificed, as well as extra damage equal to 1d4 points x the level of the spell sacrificed. The bonus you add to your attack rolls from this feat cannot be greater than your base attack bonus.
For example, A bladesinger has a base attack bonus of +11 and the ability to cast 4th-level arcane spells. On his turn, he chooses to sacrifice one of his 4th-level spells for the day, marking it off as if he had cast it. Until his next turn, he gains an extra +4 bonus on his attack rolls and an extra 4d4 points of damage with a single melee weapon of his choice (his rapier).
Source: Complete Warrior, page 96.