Weapon Finesse

Type: General
Source: Player's Handbook v.3.5

You are especially skilled at using a certain weapon, one that can benefit as much from Dexterity as from Strength. Choose one light weapon. Alternatively, you can choose a rapier, provided you can use it in one hand, or a spiked chain, provided you're at least Medium-size.

Prerequisite: Proficient with weapon, base attack bonus +1 or higher
Benefit: With the selected weapon, you may use your Dexterity modifier instead of your Strength modifier on attack tolls. Since you need your second hand for balance, if you carry a shield, the shield's armor check penalty apply to your attack rolls.
Special: You can gain this feat multiple times. Each time you take the feat, it applies to a new weapon.

For Spell Casters: You can designate touch spells as light weapons so as to add your Dexterity modifier on your melee attack rolls with such spells.