Improved Single Weapon Fighting (3.5e Feat)
From D&D Wiki
Improved Single Weapon Fighting [General (Fighter)]
You have trained even further with wielding a single weapon, becoming faster.
Prerequisite: Dexterity or Strength 17, Base Attack Bonus +6, Single Weapon Fighting
Benefit: When fighting with a one-handed or light melee weapon and nothing in the other, you gain +2 to AC and to attack. In addition, you gain an extra attack at your highest attack bonus as part of a full-attack. You take a -2 penalty for all attacks that round.
Special: The AC bonus does not apply when caught unaware or flat-footed. Stacks with Single Weapon Fighting.