Quest Chains
Guides about quest chains and generally difficult quests.
Razelikh the Defiler
The quest chain which ultimately sends you to battle the dreadlord Razelikh, is possibly the longest quest-chain in the game. It takes place in the Blasted Lands, Aszhara, Stranglethorn Vale and then back to the Blasted lands again. The first parts can be done solo at lvl 60, but this chain truely shines if you get someone to duo it with (up until the final part which require a group). The rewards at the end aren't that great, expect for a 16-slot back, but while doing this quest you will get loads of xp (if you're not yet 60) and loads of cash (after 1.10 if you're at lvl 60).
The first time I did this chain was with my 60 warrior, and with a 58 warlock tagging along. We spent a few hours doing it all except for the last two parts, he leveled half a level, I made over 50g. And if you're a lore lover, these quests provides one of the best in the game. You get to kill a dreadlord of the burning legion, for crying out loud:-)
Now, with this small guide, I'll take you through every step of the quest-chain and you'll know all you need to aquire the weapon you need, how to summon and ultimately defeat him.
Note: I have only completed this quest with alliance characters. From what I understand it's about the same for horde with minor differences.
Your first task will be to speak with Ambassador Ardalan atop the mage tower at Netergharde Keep in Blasted Lands. He will give you the first quest.
Petty Squabbles
He tells you to speak with the Fallen Hero of the Horde, who is located in Swamps of Sorrow at the entrance to the Blasted Lands(loc. 34,64). Go there and get the next part:
A Tale of Sorrorws
Simply require you to go through the dialogue with the Fallen Hero. When you have, the quest will complete and you get the follow-up:
The Stones that Bind Us
Now this is where the fun starts. The Fallen hero wants you to kill (and release from bondage) 3 Servants of Grol, 3 Servants of Allistarj, 3 Servants of Sevine and 9 Servants of Razelikh.
The servants are located as follows:
Servants of Sevine are found around and close to the Altar of Storms (39,45). Avoid Sevine herself, she is immune to almost every spell and can't be killed yet anyway.
Servants of Grol are located outside Dreadmaul Hold (don't go inside, Grol is there and same rule goes for him as for Sevine).
Servants of Razelikh are found at the edge of the crater to the Dark Portal, all along it. Don't worry, Razelikh himself is nowhere near:-)
Servants of Allistarj are found outside and in Serpents Coil (65,33). Don't go too far inside or you'll find both Allistarj himself and a giant elite felhound.
Now near everyone of these mobs there are crystal stones floating in the air, and they are the key to defeating them. Get them low on health first and then click the stone and give the killing blow. They must be within range of the stone for the effect to take place and YOU CANNOT KILL THE SERVENT WITHOUT USING THE STONE FIRST. Believe me, these servants have been kited to Stormwind by people not doing the quest, and there is no guard or racial leader in the game that can kill these guys without using the stones.
Once you have freed the required number of servants, return to the Fallen Hero and get the follow-up:
Heroes of Old
Another simple turn-in, talk to Thund Splithoof, accept the follow-up and loot your reward from the chest. It is a trinket which give u a 5 hp/5s and 5 mana/5s regen bonus.
Note: These two turn-ins alone should net you a nice 9k xp, so focusing on this quest-chain only is no killer for your xp-rate.
Now go get the new quest from the Fallen hero:
Kirith
He asks you to find an old buddy of his who he last saw tortured during their imprisonment. Kirith is actually transformed into a giant felhound, and is located in Serpents Coil where you killed Servants of Allistarj earlier. He is a lvl 55 elite at the end of the cave (if you took a left and ended up facing Allistarj himself you went too far). You need to kill him and talk to his spirit. It's doable solo with some classes, but with two or three lvl 58+ it should be fairly manageable. Just don't get any adds. If you come there after he's recently killed, you can still talk to his spirit and complete the quest (at least pre 1.11). Kirith gives you the follow-up:
The Cover of Darkness
Simply return to the Fallen Hero with a message from Kirith. Then get the next part:
The Demon Hunter
The Fallen Hero of the Horde sends you to Azshara to speak with a demon hunter named Loramus Thalipedes. He is located on an island in Northwestern Azshara, location 60,66. Get som swim pots for this one. When you find him you get a follow-up:
Loramus
Just pretend to listen to his story while you drink some tea and click "next".
Breaking the Ward
More standing around while Loramus does some ritual. When he's done you get the follow-up:
The Name of the Beast
Loramus tells you to find Lord Arkkoroc in Azshara. He is located in a ruined temple in northern Azhara, location 77,42. He gives you the next quest:
The Name of the Beast
You need to killa hydra named Hetaera. She is a 58 elite and roams the waters off the coast of Azshara. The easier way to kill her, to avoid nearby giants, is at an island at 56.44. She is soloable by skilled players of various classes, but two or more is recommended. Once she is dead loot her heads and go back to Arkkoroc:
The Name of the Beast
Go back to Loramus.
Azsharite
Now you need to collect giant shit. Not big chunks of shit, but crystals that giants pop out from their heavy diet of rock and stone. They are looted off the ground in southern Azshara, at the cliffs high up from the shore, and can be hard to spot. Luckily you are given a felhound for this quest, which you can command to locate nearby crystals. Loot 20 of them while watching out for elite giants in the area, and go back to Loramus.
The Formation of Felbane
Go see Galvan the Ancient in Stranglethorn Vale. He gives you the next quest:
Enchanted Azsharite Fel Weaponry
Just wait for Galvan to create your weapon and the choose between a dagger, a staff and a sword. They all have +AP on demons and the ability to weaken Razelikh and his servants. Afterwards he gives you the quest:
Return to the Blasted Lands
Go back to the Swamps of Sorrow and speak with The Fallen Hero of the Horde.
Uniting the Shattered Amulet
Now you must kill Sevine, Grol and Allistarj. To make it easy, get a full five-man party together. Use your newly forged Felbane sword/staff/dagger on them to make them killable (sword ability has 3 minute cooldown). Grol hits like a truck, Sevine summons elementals and is fire/shadow immune and Allistarj does some hefty spell dmg (use sword to interrupt casting on both the latter). With five people it should be piece of cake. Loot their piece of the amulet and go back to the Fallen Hero for the final quest. Time to kick some demonic ass!
You are Rak'likh, Demon
You're at the end, finally. Now you have to kill Rezelikh himself. He is atop the mountain in the middle of the Blasted Lands, and you need the amulet you just put together to get to the top. Once there, summon the demon on the alter. You need AT LEAST a five-man party to kill him. He is immune to every debuff/crowd control in the book. Warlock dots are a waste of mana on him, he is also shadow and fire immune or at least highly resistant. So a warlock is next to useless here (fear/banish doesn't work either), and mages are left spamming frostbolt and arcane missiles.
During the battle he summons two adds (one at a time), kill them fast while the tank keeps Razelikh busy. They are elite when it comes to dps, but not in hitpoints. The tank needs to position himself well as he will get lots of knockbacks and can go off the mountain and splat. There is a way to kite the demon down the mountain without getting killed. This won't stop him from summoning the adds, but at least you won't have to worry about being knockbacked to death anymore. I haven't tried this myself though, search the web for more info on this tactic.
Once he is dead, get your rewards (you get all 3): A trinket with +3 defense, +10 shadow resistance and +3 health regen, a neck with +10 fire and shadow resistance and a 16 slot bag.
Congratulations, you have completed the longest quest-chain in the game (yes, it is longer than the Onyxia-key chain, it just doesn't take that much work to complete). Be proud of yourself and whoever helped you on the way, take a screenshot of the dead demon and hang it on your wall, and then go drink some champaign and get laid. Cheers!
Tarciryan
The Battle of Darrowshire
Introduction
What seems to be a little quest about finding a little girl turns out to be one of the biggest battles in the Eastern Plaguelands.
Walkthrough
Step 1:
First, go to Winterspring, Everlook inside one of the buildings you can get the quest, Sister Pamela.
Or you can go to Sorrow Hill in Western Plaguelands and start the quest in some house. I think the name is the same atleast.
Travel to Eastern Plaguelands. If you fly to Light's Hope Chapel, follow the main road not far for it to the west. If you come from Western Plaguelands, follow the main road to the east until you reach a fork, turn south and keep going until you reach Darrowshire, Pamela shouldn´t be far away.
Pamela asks you to get her doll. The pieces of it can be found in the houses around the place. It´s some guys that are invisible/spawns when you loot the doll parts. (I can´t remember, you might have to rightclick some part to create the doll 
)
Return to Pamela with the doll and get the next quest, Auntie Marlene.
Step 2:
You can find Marlene at Sorrow Hill, just south-east of Andorhal, turn in and get the next quest, A Strange Historian.
Get the ring from the grave outside her house and bring it to Chromie, in Andorhal, not far from where you enter if you enter at the south-west entrance. Turn in and get the next quest, The Annals of Darrowshire.
Step 3:
Go to the town hall there (the one with a clock thingy) you can sneak into the place and loot the book.
There will be several tomes there, Jame showed a trick to find out which one is the right one.
Get back to Chromie, turn in and get, Brother Carlin.
This quest chain is unlocked after you complete all 3 of the quests Triton Fordring has to offer you. For this quest you are given a Scarlet Crusade uniform (Druids, mess around with shapeshifting! It's kinda cool..) which causes all Scarlet Crusaders to be friendly to you. This'll allow you to enter hearthglen solo, quickly, without getting attacked.
You can also do the last part of Unfinished Business at the same time.
Step 4:
Travel to Light's Hope Chapel, turn in and get the next quest, Villains of Darrowshire and Heroes of Darrowshire.
The skull can be found in Blackwood Lake, and the sword is found in the Infectis Scar, at both places there are some ghosts fighting.
The shield can be found east of the barn at Gahrron's Whithering. The libram can be found in city hall at Heartglen (building with clocktower) at the back. I suggest getting a group for this if you don´t have any pet or something, or do the quests at Umi in Winterspring, Everlook and use the yeti as a pet for you.
Go back and turn in the quests and get the next, Marauders of Darrowshire.
Step 5:
Go north of Light's Hope Chapel and start killing the Champions, use the crystal when you get a skull. Keep doing so until you got 5 Resonating Skulls. Go back and turn in the quest and the next quest, Return to Chromie.
Step 6:
Go back to Chromie (you know he is, right? 
) turn in the quest and get the next one, The Battle of Darrowshire. (This quest can be and should be, done in a raid. It´s doable without but hard. Atleast what I read about it)
Now, participate in the battle and make sure that:
- 1) Davil survives until Horgus dies.
- 2) Captain Redpath survives until Redpath the corrupted appers.
Step 7:
If you are succesful with the battle, talk to the spirit of Joseph Redpath and then go back to Pamela, turn in and get the last quest in this chain, Hidden Treasures.
Pamela will give you a key, with it you can open a chest behind the house and get your rewards for the effort!
When you open the chest, you will get: Magebane Scion, Ring of Protection and Archlight Talisman
The Black Knight
The Black Knight quest chain was introduced in patch 3.1 together with The Argent Tournament. Depends on you're horde or alliance, the quest will lead you to either Westfall or Silverpine Forest. The guide will unlock the known group daily for The Argent Tournament: Threat from Above.
Step 1:
Get the quest from Crusader Rhydalla at the Argent Pavilion in the Argent Tournment grounds, north-east in Icecrown.
[80] The Black Knight of Westfall? if alliance, or [80] The Black Knight of Silverpine? if horde.
Step 2:
If Alliance: Go to Moonbrook in Westfall, the book you need for the quest is in the house close to the stables (see This picture from Thottbot)
If Horde: You will have to loot a book in Valgan's Field in Silverpine Forest. The book can be found in the southern house, on the first floor ( watch this from Thottbot).
When you're done, turn in the quest back at The Argent Tournament Grounds.
Step 3:
Get the follow up; [80] The Seer's Crystal, you'll have to kill an Unbound Seer in Crystalsong Forest. They can be found around 46,42 - A bit east of Dalaran City. Kill the unbound Seer, and loot he's crystal. When you're done, turn it in at Argent Tournament.
Step 4:
Get [80] The Stories Dead Men Tell which becomes availible to you.
You can complete this quest by looting the 3 corpses at the graveyard just east of The Argent Tournament Grounds. Loot the 3 corpses, and turn it in.
Step 5:
Get [80] There's Something About The Squire. You'll have to find the Black Knight’s Squire which can be found in the Forlorn Woods in Crystalsong Forest. Kill Skeletal Woodcutters nearby until you loot a femur. Stand behind the squire and use the femur to *sap* him. Loot him then return to the Argent Tourney grounds to turn it in.
Step 6:
You should now be able to get [80] The Black Knight’s Orders. First you need to get the Black Knight's gryphon. You can find it here. Talk to it, and it will automatical fly you to the tent. Inside the tent, you'll find some Cult of The Damned members, kill them and loot the invitation and the orders. They are in the end of the tent.
When you're done, fly back on either the gryphon or your flying mount (if any).
Step 7:
==Note== You can't continue the questline before you are Champion with atleast one faction. Of course you can continue when you've earned the Champion rank.
If you're Champion, get [80] The Black Knight’s Fall. You will have to fight The black Knight in this quest. Before you can do that, you must have the Argent Warhorse. It can be found near the Champion Ring, get on it, and get ready to fight Black Knight. Go to Squire Cavin on the north side of the Champion Ring to summon The Black Knight. Defeat him - he's easy, and turn it in when you're done.
Step 8:
When you've turned in [80] The Black Knight’s Fall, get the follow up; [80] The Black Knight's Curse. Go to the graveyard (like in a previous quest) and right click The Black Knight's grave for a short dialog. There will spawn some Cult of the Damned members, kill them and you're done with [80] The Black Knight's Curse.
Step 9:
[80] The Black Knight's Fate is the last quest in the long Black Knight chain. You will have to find Doctor Kohler and kill him, he can be found at Deathspeaker's Watch west of The Argent Tournament Grounds. The Doctor is near the altar in the middle of Deathspeaker's Watch.
The Black Knight quest chain ends here, you can fight him in the The Crusader's Coliseum, as the final boss in Trial of the Champion.