Arcane Tome

Arcane Tomes, along with Firewing Signets and Sunfury Signets, are items used to get reputation with the Scryers in Shattrath City.

Source
This item is dropped by higher level blood elves in Shadowmoon Valley, Netherstorm, and the Isle of Quel'Danas. Contrary to popular belief, blood elves in Firewing Point also drop Arcane Tomes, despite the description of Synthesis of Power, which clearly states that they drop from higher level mobs.

As a quest objective

 * Synthesis of Power
 * Arcane Tomes (Repeatable)