Sha'tar is the name the Aldor call the Naaru. Many quests in
Shattrath City, Nagrand, Auchindoun: Shadow Laberynths dungeon-wing,
and Netherstorm may help you increase reputation with the Sha'tar.
Additionally, blood elves in Shadowmoon Valley drop signet of
Kael'thas, which can be turned in to an NPC to gain Sha'tar reputation.
Not only can you get great rewards, you can also obtain recipes and a
key to unlock the Heroic mode of Tempest Keep instances for an enhanced
loot table. The NPC vendor granting Sha'tar rewards is
Almaador (Sha'tari Quartermaster). You may find him at the Terrace of Light in Shattrath City.