Storm Bolt

 
Prerequisite(s): Ability to cast 3rd level spells.
 
Benefit: As long as you have an electricity spell of 3rd level or higher available to cast, you can fire a 20-foot line of electricity as a standard action. This bolt deals ld6 points of electricity damage per level of the highest-level electricity spell you have available to cast. As a secondary benefit, you gain a +1 competence bonus to your caster level when casting electricity spells.
 
Source: Complete Mage