As many Leatherworkers will know, once you reach level 40 and have a skill level of 225, you are able to specialise in a branch of Leatherworking. I’ve seen so many people asking "What type of Leatherworking should I take?" that I decided to make a small guide to advise you how to spec depending on your class (NB: This assumes that the majority of people who take LW are going to be Rogues, Hunters, Shaman or Druids; the 4 classes who can wear leather armour from level 1).
Note that the NPC Leatherworkers mentioned here will only teach the specialisation (Tribal, Dragonscale or Elemental), which will determine what items you can make after passing 225 in Leatherworking. In order to pass 225, you will still need to train in Artisan Leatherworking - the Alliance will need to speak to Draak Stonehand in Aerie Peak in the Hinterlands, and the Horde will have to find Hahrana Ironhide in Camp Mojache in Feralas. You can learn Artisan Leatherworking at level 35. It costs 5 gold.
Please be aware that once you choose your specialisation by completing the respective quests, it will be impossible to obtain either of the other 2 paths, even if you drop Leatherworking and then take it again.

Dragonscale:
Primarily for Shaman, as this type of LW produces mail, which they can use post-40. Gives some good +STR/+STA bonuses. Can also be used by Hunters, who can also use mail after level 40. However, note that none of the lines seem to really tailor for the Hunter class. I suggest Dragonscale for 2 reasons - 1 is that it produces mail armour. The second is that the Black Dragonscale armour is amazing for this class.
Note that Dragonscale Leatherworking has the longest quest to specialise out of any of the 3 trees.

Trainer recipies:
Dragonscale Breastplate - http://www.thottbot.com/?i=3978
Dragonscale Gauntlets - http://www.thottbot.com/?i=3668

Drops and vendor recipies:
Red Dragonscale (Fire resistance boost, and a boost to healing spells and effects)
Breastplate - http://www.thottbot.com/?i=25219

Green Dragonscale (SPI and STA boosts, as well as a Nature resistance boost. Set bonuses give mana/sec regen and mana regen while casting)
Breastplate - http://www.thottbot.com/?i=8246
Leggings - http://www.thottbot.com/?i=14948
Gauntlets - http://www.thottbot.com/?i=52007

Blue Dragonscale items (INT, and a small bonus to SPI and Arcane resistance. Set bonus gives a minor multiple-resistance boost and a bonus to damage/healing spells)
Breastplate - http://www.thottbot.com/?i=18346
Shoulders - http://www.thottbot.com/?i=17029
Leggings - http://www.thottbot.com/?i=51994

Black Dragonscale (STA and Fire resistance bonuses. Hunters love these items for the massive Attack Power bonus that they provide (a total of +172 AP). Set bonuses contributes to Hit% and Crit%, and a minor Fire resistance boost)
Breastplate - http://www.thottbot.com/?i=5359
Shoulders - http://www.thottbot.com/?i=15340
Leggings - http://www.thottbot.com/?i=17027
Boots - http://www.thottbot.com/?i=28132

Chromatic Cloak (epic) - http://www.thottbot.com/?i=36124
Chromatic Gauntlets (epic) - http://www.thottbot.com/?i=40773

To specialise in Dragonscale Leatherworking you will need to complete the Dragonscale Leatherworking quest from Thorkaf Dragoneye <Master Dragonscale Leatherworker> in the Badlands for the Horde, or Peter Galen <Master Dragonscale Leatherworker> in Azshara for the Alliance.
This quest require you to bring 2 Tough Scorpid Breastplates, 2 Tough Scorpid Gloves, and 10 Worn Dragonscales to the quest giver.

Elemental:
There are some good +agi items in the Helm of Fire, Gauntlets of the Sea and Shifting Cloak (epic drop for the plans however) in this line, which makes it ideal for Rogues. The Stormshroud Set is also very nice for this class.

Trainer recipies:
Gauntlets of the Sea - http://www.thottbot.com/?i=17499
Helm of Fire - http://www.thottbot.com/?i=5299

Drops and vendor recipies:
Living set {STA and SPI bonuses, as well as a small Nature resistance. Also a boost to healing spells makes this set nice for Druids)
Breastplate - http://www.thottbot.com/?i=27867
Shoulders - http://www.thottbot.com/?i=23745
Leggings - http://www.thottbot.com/?i=18162

Stormshroud Set (decent bonuses to dodge and crit chances and also a STA boost)
Armour - http://www.thottbot.com/?i=25540
Shoulders - http://www.thottbot.com/?i=25586
Pants - http://www.thottbot.com/?i=18575

Volcanic Set (provides Fire resistances. Also one of the highest armour leather sets in the game)
Breastplate - http://www.thottbot.com/?i=15846
Shoulders - http://www.thottbot.com/?i=25895
Leggings - http://www.thottbot.com/?i=8321

Molten Helm (epic) - http://www.thottbot.com/?i=27836
Molten Belt (epic) - http://www.thottbot.com/?i=40689
Shifting Cloak (epic) - http://www.thottbot.com/?i=36198

Be warned that most of the patterns from Elemental LW require large quantities of low-drop rate items (e.g. 2x Core of Earth, 2x Breath of Wind, 2x Heart of Fire etc).

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I think by far the best way of getting the essences and the cores of earth, hearts of fire and globes of water is to take advantage of the elemental invasions. These are as follows:
- Water: Winterspring
- Air: Silithus
- Fire: Un Goro
- Earth: Azshara

The drops rates are (although still low) "decent" as far as elementals go and you will be finding elementals in good numbers as well.
Also if you have friends that can help you is worth going for the elite elemental boss that leads the invasions since they have a very high drop rate and usually drop more than one essence Princess Tempestia in WInterspring dropped me 2 essence of water!)

All you need to do is check when each elemental invasion takes place. 5hrs in total, of farming in SIlithus if the elementals there got me 11 Essences of Air. The invaders are considerable weaker that the Stormers there….almost 1k health less, nolighting shields and no spells and have a drop rate of around 5-6%….and that is high for elementals! Now I am currently waiting for the water invasion to stack up on some water essences. :)

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To specialise in Elemental Leatherworking, you will need to complete a quest given by Brumn Winterhoof <Master Elemental Leatherworker> in the Arathi Mountains for the Horde, or Sarah Tanner <Master Elemental Leatherwoker> in the Searing Gorge for the Alliance.
This quest requires you to bring 2 Hearts of Fire, 2 Globes of Water, 2 Cores of Earth, and 2 Breaths of Wind to the quest giver.

Tribal:
In my opinion, this is the "Druid branch" of Leatherworking, what with one of the first items you can purchase from your trainer (the Wolfshead Helm) giving bonuses to Druid shapeshifting abilities. A multitude of stat boosts here:

Trainer recipies:
Wolfshead Helm - http://www.thottbot.com/?i=5056
Feathered Breastplate - http://www.thottbot.com/?i=8313

Drops and vendor recipies:
Chimeric (good Arcane/Nature resistances)
Vest - http://www.thottbot.com/?i=21254
Gloves - http://www.thottbot.com/?i=24861
Leggings - http://www.thottbot.com/?i=39823
Boots - http://www.thottbot.com/?i=19010

Frostsaber (shadow/frost resistances)
Tunic - http://www.thottbot.com/?i=25846
Gloves - http://www.thottbot.com/?i=25846
Leggings - http://www.thottbot.com/?i=17438
Boots - http://www.thottbot.com/?i=14790

Warbear (STA and STR bonuses (nice for feral Druids))
Harness - http://www.thottbot.com/?i=16155
Woolies - http://www.thottbot.com/?i=9920

Ironfeather set (SPI/INT bonuses (as mentioned by Eldoras, these are nice items for Restoration specced Druids))
Breastplate - http://www.thottbot.com/?i=9920
Shoulders - http://www.thottbot.com/?i=9253

Devilsaur set (STA, attack power, and crit chances. A fairly nice set for Rogues, Hunters and Feral Druids)
Gauntlets - http://www.thottbot.com/?i=5111
Leggings - http://www.thottbot.com/?i=5056

Corehound Belt (epic) - http://www.thottbot.com/?i=40678
Corehound Boots (epic) - http://www.thottbot.com/?i=27559
Hide of the Wild (epic) - http://www.thottbot.com/?i=36157

Please note that many people consider Tribal leatherworking to be the money-making specialisation, as the items required for the good patterns (e.g. Devilsaur Leggings/Gauntlets) are much more farmable than dragon scales or essences.

Note that to specialise in Tribal Leatherworking you will need to complete the Wild Leather quest chain (obtained from Jangdor Swiftstrider in Camp Mojache, Feralas, for the Horde, or Pratt McGruben at the Feathermoon Stronghold, Feralas, for the Alliance). However, the Wild Leather patterns are not Tribal Leatherworking specialities - the quests for them are merely pre-reqs for becoming a Tribal leatherworker. Completing the Wild Leather quests does not force you to specialise in Tribal, either, meaning that you can complete them as an Elemental or Dragonscale leatherworker also.
You must then complete the Tribal Leatherworking quest from Se’jib <Master Tribal Leatherwoker> in Stranglethorn Vale for the Horde, or Caryssia Moonhunter <Master Tribal Leatherworker> in Feralas for the Alliance.
The Tribal Leatherworking quest requires you to bring a Wild Leather Vest and a Wild Leather Helmet to the quest giver.

Tribal for Rogues
This has been bought up numerous times on pages 3 and 4 of the thread - Rogues are after Devilsaur equipment, which, I must admit, is very attractive to this class. Whilst it is fully up to you which branch of Leatherworking you take, I would say not to take up one of these subclasses based on 1 item or item set. You can usually buy these items from Leatherworkers who have already specialised in these branches, which leaves you free to progress down a tree more suited to your class (in this case, Elemental).

Listed below are the names and locations of each of the various mobs you have to kill to get the items for each of the 3 quests (Dragonscale, Elemental, Tribal)

Dragonscale

Scorpid scales (required to make the Tough Scorpid Breatplate and Gloves) are obtained from drops and skinning a variety of Scorpids, notably:
Deadly Cleft Scorpids in Uldaman (levels 37-42)
Scorpid Hunters and Tail Lashers in Tanaris (levels 40-43)
Scorpid Dunestalkers in the Hillsbrad Foothills (levels 46-47)
Scorpok Stingers in the Blasted Lands (levels 50-51)
and Scorpid Deepstingers in BRD (levels 50-52)

Worn Dragonscales can be found from:
Scalding Whelps in the Badlands (levels 41-43)
Sprite Darters in Feralas (level 43-45)
Black Broodlings, Dragonspawn, Drakes and Wyrmkin in the Burning Steppes (levels 51-54)
Blue Scalebanes and Dragonspawn in Azshara (levels 51-53)
Cobalt Broodlings, Mageweavers, Scalebanes, Whelps, and Wyrmkin in Winterspring (levels 54-57)

Elemental:

Hearts of Fire can be found on:
Blazing Elementals, Inferno Elementals and Magma Elementals in Searing Gorge (levels 45-49)
Blazing Fireguards in BRD (levels 45-54)
Scorching Elementals and Living Blazes in Un’Goro Crater (level 53-55)

Breaths of Wind can be found on:
Gusting Vortexes in Tanaris (43-45)
Dust Stormers in Blackrock Mountain (levels 55-57)
Cyclone Warriors, Dust Stormers and Whirling Invaders in Silithus (levels 56-58)

Cores of Earth can be found on:
Ambershard Crushers and Destroyers, Shadowshard Rumblers and Smashers in Desolace and Mauradon (levels 40-43)
Ground Pounders and Land Ragers in Tanaris (levels 41-47)
Desert Rumblers and Ragers in Silithus (levels 57-59)

Globes of Water can be found on:
Noxious Scions in Mauradon {level 46)
Sea Sprays and Sea Elementals in Feralas (levels 47-49)
Blighted Horrors and Discordant Surges in the Eastern Plaguelands (levels 54-58)

For more information on any of the quests, visit any of the below links:

Dragonscale:
Horde: http://www.thottbot.com/?q=2609
Alliance: http://www.thottbot.com/?q=3502

Elemental:
Horde: http://www.thottbot.com/?q=15905
Alliance: http://www.thottbot.com/?q=15902

Tribal:
Horde: http://www.thottbot.com/?q=4928
Alliance: http://www.thottbot.com/?q=3345

For information on the Wild Leather quest chain, please visit http://www.thottbot.com/?s=wild+leather (copy/paste link)
Also note that although the Wild Leather quests are a prequisite for the Tribal Leatherworking quest chain, any leatherworker can complete them. They are not limited to Tribal Leatherworkers.

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Have your Saltshaker ready once you hit 250 in leatherworking!
You need the shaker to convert Deeprock Salt into Refined Deeprock Salt, which is needed to make Cured Rugged Hide. As there is a 3 day cooldown on the Shaker, you can only cure one rugged hide every 3 days. So start curing those hides asap - you won’t need them until you hit about 280 in Leatherworking I believe, but you will be glad that you prepared a few hides then :)

Also, do not rely on your specialisation patterns for skillups. The Wicked and Runic leather stuff should be enough for skillups all the way up to 300, so no need to farm for hours for one skillup point.

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