Updated Thu, Feb 21, 2008 by DarkFact
From WorldOfWarcraft's site:
"This time, the attack came from the armies of Illidan Stormrage. A large regiment of blood elves had been sent by Illidan’s ally, Prince Kael'thas Sunstrider, to lay waste to the city. As the regiment of blood elves crossed the bridge, the Aldor’s exarchs and vindicators lined up to defend the Terrace of Light. Then the unexpected happened: the blood elves laid down their weapons in front of the cities defenders. Their leader, a blood elf elder known as Voren’thal, stormed into the Terrace of Light and demanded to speak to the naaru A'dal. As the naaru approached him, Voren’thal knelt and uttered the following words: “I’ve seen you in a vision, naaru. My race’s only hope for survival lies with you. My followers and I are here to serve you.”
The defection of Voren’thal and his followers was the largest loss ever incurred by Kael’thas’ forces. Nor were these just any blood elves. Many of the strongest and brightest amongst Kael’thas’ scholars and magisters had been swayed by Voren’thal's influence. The naaru accepted the defectors who became known as the Scryers. "
The Scryers is one of the factions you may choose to ally yourself with as you enter Shattrath city. Both Horde and Alliance can be Scryer, although Draenei will be Hated initially thanks to the lore and how both factions came to be. Blood Elves will be friendly immediately upon choosing Scryer.
Although there is no set best faction to support, Aldor generally favors DPS Casters with their inscriptions and the spellthread recipes at Honored and Exalted.
It is worthy of note that you cannot be on friendly terms with both factions at once. Due to the way it is set up, if you complete quests for either faction your standing with the other will lower substancially more, making it mathematically impossible for you to have favor with both at once. You will always lose 10% more than what you earn with the opposing faction.
Should you find yourself Hated or below Neutral with the Scryers, you will need to find Arcanis Adyria in Shattrath City and accept her quest, Vorenthal's Visions. This will make you go hunt Basilisks in Terokkar for their Dampscale Basilisk Eyes, and you may repeat this quest until you reach Neutral. Each turn-in of 8 eyes will net you 250 reputation with the Scryers and substract you 275 reputation with the Aldor.
Until Honored, the best way to earn reputation will be to turn in Firewing Signets, worn by lower-level hostile Blood Elves. There's a good spot to kill Blood Elves for Firewing Signets in Terokkar's Eastern Area, called Firewing Point - you will find lots of enemies there to farm Firewing Signets with, and a low possibility for Arcane Tomes as well. 240 Signet turnins will get you to Honored.
Once you have reached Honored, you can choose to complete as many quests as you can for the Scryers, including and most importantly the lengthy line in Netherstorm's Area 52 - you will also be able to turn in Sunfury Signets and Arcane Tomes by now. Sunfury Signets act the same way as Firewing Signets but should only be turned in from Honored and above. Arcane Tomes will net you 350 reputation each, and will get you some runes needed to buy some of the Scryer inscriptions.
As a Scryer, you will want to visit Tempest Keep's 5-mans as often as you can for Sunfury Signets and Arcane Tomes. Since most of the enemies in both the Botanica and The Mechanar are Blood Elves, they will have a very high droprate for your needed items.
Quests - ~6000 Reputation - Netherstorm Line, Shadowmoon Valley Lines
Firewing Signet - 25 reputation per, 250 per 10. Only good until Honored.
Sunfury Signet - 25 reputation per, 250 per 10. Good until Exalted.
Arcane Tome - 350 reputation per. Good until Exalted
The best places to farm for Signets and Tomes are spread out all over Outland. While many would think that Netherstorm is the best place for it since the Manaforges have large concentrations of Blood Elves, the best and most often ignored place to get Sunfury Signets and Arcane Tomes is Shadowmoon Valley, there's a Bloodelf Camp to the east of the Alliance Town in Shadowmoon that's not very crowded, and has level 70 Blood Elf enemies for you to kill.
The Mana Forges are of course great, but do avoid the north-western Manaforge as it has more demons than Blood Elves.