Source: Compete Warrior
You can channel arcane energy into your melee attacks.
Prerequisite: 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 tolls 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, Yarren the 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, Yarren 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).