Dungeons & Dragons 3.5 Feat: Power Attack

You can make exceptionally powerful melee attacks

Str 13

on your action, before making attack rolls for a round, you may choose to subtract a number from all melee attack rolls and add the same number to al melee damage rolls. This number may not exceed your base attack bonus. The penalty to attacks and bonus to damage apply until next turn.

If you attack with a two-handed weapon or with a one handed weapon wielded in two hands, instead add twice the number subtracted from your attack rolls. Can't add the bonus from power attack to the damage dealt with a light weapon (except with unarmed strikes and natural attacks), even thought the penalty on attack rolls still applies, (normally, you treat a double weapon as a one-handed weapon and a light weapon. If you choose to use a double weapon like a two handed weapon, attacking with one end of it in a round, you treat it as a two-handed weapon)
A fighter may select Power Attack as one of his fighters bonus feats (PH 38)