Flask of Supreme Power

Another useful flask for end-game raiding, this recipe drops off Ras Frostwhisper in the Scholomance.

Very useful for caster dps including mages, warlocks, balance druids, and shadow priests.

I know your comment is over a year old, but for anyone not paying attention I'd point out that this flask now does straight +70 spellpower; as such, it is useful for healers as well.

The new caster flasks (Pure Death and Blinding Light) give +10 more spell damage but are limited to certain spell types (Pure Death is Shadow/Fire/Ice and Blinding is Holy/Nature/Arcane). Depending on your class and spec this flask might be better or worse than those ones. Some mages switch between Arcane and Fire/Ice a lot so maybe they might like Supreme Power better, however Warlocks only really need Fire/Shadow so they may like Pure Death...Balance Druids only need Nature/Arcane so they may like Blinding Light.