Ready Shot( Heroes of Battle, p. 99)
You can make devastating attacks with ranged weapons against charging opponents.
Point Blank Shot (PH) ,
You can ready an action to fire a ranged weapon at a foe who charges you. You must wait until the target is within 15 feet before you attack. If you score a hit with this readied attack, your attack deals an extra 3d6 points of damage. Creatures immune to extra damage from critical hits are immune to this effect.