Raining Lightning - Artificer's
First, an artificer must gain the ability to apply a metamagic feat he knows to a spell trigger item (generally a wand). He must have the appropriate item creation feat for the spell trigger item he is using. Using this ability expends additional charges from the item equal to the number of effective spell levels the metamagic feat would add to a spell. Then you have a 9th level Lightning bolt wand made by a 9th level artificer. How to pump that up is you get Wand Mastery feat which raises the wands effective caster level +2 which makes it effectively a 11d6 lightning bolt.
Note, its possible practiced spellcaster feat could make this nastier.
Now we employ the feat chain quicken(4 levels) + twin(4 levels) + empower (increase variable numeric effects by 50%, +2 levels) + maximize (+3/level) with the wands, so since we are quickened it uses a bonus or swift action, and then we repeat (minus quicken) for our standard action + Dual Wand Wielder.
Swift Action(Quicken and Twin + 2 wands): 9th level lightning + wand mastery = 11d6 + empower = 16d6 + maximize = 96 damage * 4(bolts from quicken, 2 wands, and twin)
Standard Action (Twin + 2 wands): same as above 4 more bolts * 96 damage.
Total of 8 lightning bolts * 96 damage.
Charge Break Down: 13 charges + 1 for the spell effect * 2 ( 2 wands) * 2 (swift action-quicken + regular action) = 56 total or 28 charges per wand.
There you have it.