Ambidexterity( Player's Handbook 3.0)
You are equally adept at using either hand
Greater Two-Weapon Fighting (ELH) ,
You ignore all penalties for using an off hand. You are neither left-handed nor right-handed.
This feat helps offset the penalty for fighting with two weapons.
See the Two-Weapon Fighting feat, page 86, and Table 8-2:Two-Weapon Fighting Penalties, page 125.
A ranger wearing light armor or no armor can fight with two weapons as if he had the feats Ambidexterity and Two-Weapon Fighting.
Without this feat, a character who uses his or her off hand suffers a -4 penalty to attack rolls, ability checks, and skill checks.
For example, a right-handed character wielding a weapon with her left hand suffers a -4 penalty to attack rolls with that weapon.