Warlock quests

Alliance

 * Lago Blackwrench. Warlock quest giver in Ironforge in The Forlorn Cavern.
 * Gakin the Darkbinder. Warlock quest giver in Stormwind City in The Slaughtered Lamb's basement (in the Mage Quarter).

Neutral

 * Strahad Farsan. A quest NPC in Ratchet in The Barrens.
 * Menara Voidrender. A quest NPC in Ratchet in The Barrens.
 * Niby the Almighty. A lunatic Warlock in the Shatter Scar Vale in Felwood.
 * Impsy. An Imp in the Shatter Scar Vale in Felwood, Niby's Minion.

Introductory Quest
This is your first quest that is class exclusive. Simply take the Tainted Item to the person noted in the quest text. They are not far away.
 * (Northshire Valley)
 * (Coldridge Valley)
 * (Valley of Trials)
 * (Tirisfal Glades)
 * (Sunstrider Isle)

Summoning of the Imp
There are no longer any quests to summon the imp pets. It is now trainable from the starting zone warlock trainer at level 1. Previously, the person that you delivered the Tainted Item to had a quest for you, to get:
 * IconSmall Orc Female.gif 6 Vile Familiar heads by killing and looting Vile Familiars by the cave to the north.
 * IconSmall Undead Female.gif 3 Rattlecage Skulls by killing and looting Rattlecage Skeletons on the north side of Deathknell.
 * IconSmall BloodElf Female.gif 4 Wraith Essence and 1 Tainted Wraith Essence by killing and looting Arcane Wraiths and Tainted Arcane Wraith in Falthrien Academy to the west.
 * IconSmall Human Female.gif The book Powers of the Void, near a Defias tent in the Vinyards across the river.
 * IconSmall Gnome Female.gif 3 Feather Charms by killing and looting Frostmane Novices in a cave to the southwest.

The reward for this quest was the spell Summon Imp.

Summoning of the Voidwalker

 * (Stormwind, Mage Quarter)
 * (Elwynn Forest, Goldshire)
 * (Tirisfal Glades)
 * (Durotar)
 * (Tirisfal Glades)
 * (Durotar)
 * (Durotar)
 * (Durotar)

Summoning of the Succubus

 * (Alliance) (Alternative start of Questline: in Ironforge)
 * (Horde, Undercity)
 * (Horde, Orgrimmar)
 * (Horde, Undercity)
 * (Horde, Orgrimmar)
 * (Horde, Orgrimmar)
 * (Horde, Orgrimmar)

Rewards
 * Summon Succubus
 * Summon Succubus

Summoning of the Felhunter

 * (Stormwind, The Slaughtered Lamb)

Rewards
 * Summon Felhunter
 * Summon Felhunter

Summoning of the Infernal
There is also a warlock item-quest located in Shatter Scar Vale obtained at level 52 at your warlock trainer.
 * - Starts at Niby the Almighty in Shatter Scar Vale

Rewards
 * Inferno
 * Inferno

Summoning of the Doomguard
This questline ends up teaching you the Ritual of Doom to summon a Doomguard. This is the same Doomguard as is summoned by the Curse of Doom which has a 10% chance to summon the Doomguard, but it always summons a Doomguard in a ritual that need 5 players and randomly sacrifices one of them.


 * (Blasted Lands, Daio the Decrepit)
 * (Blasted Lands, Daio the Decrepit)

Summoning of the Felsteed
The Summon Felsteed spell no longer requires a quest, and can be learned from a Warlock Trainer at level 20. (Used to be level 40 until patch 2.4.3)

Summoning of the Dreadsteed
This quest is no longer required, as Dreadsteed is a trainable ability available at level 40. The Summon Dreadsteed spell can be learned from a Warlock Trainer at level 40 and requires Journeyman Riding skill. The quest allows you to obtain this spell (and the associated Feat of Strength) at level 60. This quest line consists of two independent "lines" (One gathering/crafting line and one adventuring line) that can be done simultaneously.
 * (Burning Steppes, Altar of Storms, Gorzeeki Wildeyes)
 * (Felwood, Shadow Hold, Lord Banehollow)
 * (Felwood, Shadow Hold, Lord Banehollow)
 * (Burning Steppes, Altar of Storms, Gorzeeki Wildeyes)

Cost Reward
 * (Optional items: either bought from the Goblin: J'eevee's Jar, Black Lodestone, Xorothian Glyphs, or you can ask another lock who already have these items to run you through DM West for the Dreadsteed of Xoroth quest)
 * (For Shadowy Potion)
 * (For Xorothian Stardust)
 * 3 Black Dragonscales (changed from 35 in patch 2.1)
 * 2 Elixir of Shadow Power (changed from 10 in patch 2.2)
 * 25 Dark Iron Ore
 * 6 Large Brilliant Shards
 * 1 Arcanite Bar (changed from 3 in patch 2.2)
 * Summon Dreadsteed

Items of Power
Of course, Warlocks also get item quests, this should be a complete list.

The Orb of Soran'ruk

 * (The Barrens, Ratchet)

 Rewards 

You can choose one of the following:

A Noble Brew
It seems that this questline can be done by every Alliance character, but the final and item rewarding step can only be done by a Warlock.
 * (Stormwind, The Slaughtered Lamb)

 Rewards 


 * Dread Mage Hat

Enchanted Gold Bloodrobe

 * (Stormwind, The Slaughtered Lamb)
 * (Undercity)
 * (Orgrimmar, The Cleft of Shadow)

 Rewards 
 * Enchanted Gold Bloodrobe

Orb of Orahil

 * 1) Then do one of the following quests. They are not technically prerequisites, but provide the required quest item for .  Accepting either quest will make the other unavailable.  The final chain rewards have been made identical, so it makes no difference which you accept.  NOTE: Neither of these quests have anything to do with your ability to summon either a Felhunter or an Infernal; those are completely separate quest chains(see above).
 * 2) Then she will offer
 * , if you completed, or
 * , if you completed.
 * 1) Then she will offer
 * , if you completed, or
 * , if you completed.
 * 1) Then she will offer
 * , if you completed, or
 * , if you completed.

 Rewards  (one of the following):

Niby's stuff - he doesn't need it anyhow
Impsy, Niby the Almighty's Imp minion wants to create a minion for himself - funny, but you will gain some nice items too. The Questline seems to have three alternative starts in Felwood, Stormwind and Orgrimmar.
 * (Felwood, Shatter Scar Vale, Impsy)
 * (Stormwind, The Slaughtered Lamb, Demisette Cloyce)
 * (Orgrimmar, Cleft of Shadow)

 Cost 
 * 1

 Rewards 

You can choose one of the following:

Harnessing Shadows
This is one of the book quests of Dire Maul. Just turn it in in the Library in Dire Maul.  Rewards 
 * Royal Seal of Eldre'Thalas