This faction of Ethereals is based in the Stormspire in Netherstorm, but have outposts in many other regions of Outland including Nagrand and in Auchindoun. You can increase your reputation by doing one-time and repeatable quests and by killing monsters in the Mana-Tombs within Auchindoun.
Neutral to Friendly
There are two repeatable quests available from Aeris Landing in Nagrand: Gather Crystal Fragments for Gezhe, and Ivory Tusks for Shadrek. You will also receive reputation from running Mana-Tombs.
Friendly to Honored
At Friendly, you can begin turning in Obsidian Warbeads at Aeris Landing in stacks of ten. Obsidian Warbeads are found from the ogres of Nagrand, and can also be turned in for Kurenai / Mag'har reputation. Another repeatable quest starts in Area 52 in Netherstorm, as Nether-Stalker Khay'ji wants Zaxxis Insignias found from a rogue camp of Ethereals. Runs of Mana-Tombs will also continue to grant reputation.
Honored to Exalted
Mana-Tombs will no longer grant reputation on Normal mode starting with Honored reputation. However, running Mana-Tombs in Heroic mode will continue to give reputation until Exalted. You can also continue turning in Obsidian Warbeads and Zaxxis Insignias all the way to Exalted. At this point is also a good time to do the many Consortium quests available in Netherstorm.