A post inspired by the above picture, the awesome lightning pirates in Stardust, and the fact that "mana potions" are boring.
Lightning is power. In a magic-rich environment, this is true in more ways than one (that one otherwise being "the power to fry anything stupid enough to be standing out in the open"). The wizards of the Coin long ago worked out that properly captured and processed, lightning could be used as a power source for their spell-workings. Most wizard towers have a lightning-rod and processing equipment installed, although unless the resident feels like messing with the local weather patterns or annoying a god, there's always the problem of getting a regular supply (compounded by the fact it goes flat after a while). Many wizards prefer to just buy it from the few skyship crews who specialize in lightning collection.
A bottle of reasonably fresh, refined, lightning costs about 350-400gp. It can be used in one of two ways:
Firstly, a wizard (or cleric) can drink it as a standard action. If he then casts a spell on his next turn, that spell's HP cost is reduced by 1d6. If the caster doesn't cast a spell on his text turn, however, the build-up of power discharges, dealing him 1d6 damage.
Second, it can be shaken and thrown, causing it to explosively discharge. This deals 3d6 damage to the target, and 1d6 damage to anybody standing next to him (Reflex save for half. DC = thrower's attack roll).
Stale, old, bottled lighting would use a d4 or d3 instead of a d6.