From WoWWiki
A stable master is an NPC that offers hunters the opportunity to store four pets and retrieve them at any other allied stable master. They are typically found outside most city and town inns or near the pet trainers. You can ask the city guards where they are when you are in major cities.
To stable a pet, right-click on the stable master to open the stable window. You will see your current pet displayed as an icon on the left side of the window. On the right side are four slots (two prior to patch 3.0.2). Depending on if you purchase to open the slots, they will be either active, or red to show you still need to unlock them. The cost of the stable slots is as follows: 5
for the first, 5
for the second, 50 for the third, and 150 for the fourth. Just click and drag your current pet's icon to any stable slot on the right to stable it. If another pet is in that stable slot, that will now become your active pet.
As of Patch 3.0.2 players may use stable masters to recover lost non-combat pets rewarded by quests at any stable master. Restoring a lost pet will not reward the pet item, but rather store the pets' spell directly in the pet collection. E.g. 
[Worg Pup] – Quest Reward from 
[59D] Kibler's Exotic Pets can be restored if you destroyed the item but have finished the quest.
Alliance stable masters
| Location | Stable Master
|
| Dolanaar, Teldrassil
|  Seriadne
|
| Kharanos, Dun Morogh
|  Shelby Stoneflint
|
| Goldshire, Elwynn Forest
|  Erma
|
Azure Watch, Azuremyst Isle 
|  Esbina
|
| Cenarion Enclave, Darnassus
|  Alassin
|
| Hall of Arms, the Military Ward, Ironforge
|  Ulbrek Firehand
|
| The Dwarven District, Stormwind
| Jenova Stoneshield
|
| The Park, Stormwind
| Sylista
|
| Seat of the Naaru, the Exodar
|  Arthaid
|
| Auberdine, Darkshore
| Jaelysia
|
| Thelsamar, Loch Modan
| Lina Hearthstove
|
| Sentinel Hill, Westfall
|  Kirk Maxwell
|
| Blood Watch, Bloodmyst Isle
| Astur
|
| Lakeshire, Redridge Mountains
| Penny
|
| Menethil Harbor, Wetlands
| Bethaine Flinthammer
|
| Darkshire, Duskwood
| Steven Black
|
| Astranaar, Ashenvale
| Maluressian
|
| Southshore, Hillsbrad Foothills
| Wesley
|
| Nijel's Point, Desolace
| Shelgrayn
|
| Theramore Isle, Dustwallow Marsh
| Michael
|
| Feathermoon Stronghold, Feralas
| Antarius
|
| Aerie Peak, the Hinterlands
| Killium Bouldertoe
|
| Dun Baldar, Alterac Valley
| Stormpike Stable Master
|
| Honor Hold, Hellfire Peninsula
| Master Sergeant Lorin Thalmerok
|
| Telredor, Zangarmarsh
| Joraal
|
| Telaar, Nagrand
| Luftasia
|
| Sylvanaar, Blade's Edge Mountains
| Fiskal Shadowsong
|
| Wildhammer Stronghold, Shadowmoon Valley
| Crinn Pathfinder
|
Valiance Keep, Borean Tundra 
| Celidh Aletracker
|
| Valiance Keep, Borean Tundra
| Ronald Anderson
|
| Fizzcrank Airstrip, Borean Tundra
|  Toby "Mother Goose" Ironbolt
|
| Valgarde, Howling Fjord
| Horatio the Stable Boy
|
| Westguard Keep, Howling Fjord
| Chelsea Reese
|
| Fort Wildervar, Howling Fjord
| Artie Grizzlehand
|
| Wintergarde Keep, Dragonblight
| Zybarus of Darnassus*
|
| Stars' Rest, Dragonblight
| Sentinel Sweetspring
|
| Amberpine Lodge, Grizzly Hills
| Matthew Ackerman
|
| Venture Bay, Grizzly Hills
| Tim Street
|
| Westfall Brigade Encampment, Grizzly Hills
|  Squire Percy
|
| Frosthold, the Storm Peaks
| Boarmaster Bragh
|
* Zybarus of Darnassus is only available after completion of the quest 
[72] Flight of the Wintergarde Defender
Horde stable masters
| Location | Stable Master
|
| Razor Hill, Durotar
|  Shoja'my
|
| Seikwa, Mulgore
|  Seikwa
|
| Brill, Tirisfal Glades
|  Morganus
|
| Falconwing Square, Eversong Woods
|  Anathos
|
| Valley of Honor, Orgrimmar
|  Xon'cha
|
| Lower Rise, Thunder Bluff
|  Bulrug
|
| The Trade Quarter, Undercity
|  Anya Maulray
|
| Farstriders' Square, Silvermoon
| Shalenn
|
| The Sepulcher, Silverpine Forest
| Sarah Goode
|
| Tranquillien, Ghostlands
|  Paniar
|
| The Crossroads, the Barrens
| Sikwa
|
| Camp Taurajo, the Barrens
| Kelsuwa
|
| Tarren Mill, Hillsbrad Foothills
| Theodore Mont Claire
|
| Splintertree Post, Ashenvale
|  Qeeju
|
| Sun Rock Retreat, Stonetalon Mountains
|  Gereck
|
| Freewind Post, Thousand Needles
| Awenasa
|
| Hammerfall, Arathi Highlands
| Tharlidun
|
| Shadowprey Village, Desolace
| Aboda
|
| Grom'gol Base Camp, Stranglethorn Vale
| Durik
|
| Stonard, Swamp of Sorrows
| Hekkru
|
| Kargath, Badlands
| Greth
|
| Camp Mojache, Feralas
|  Shyrka Wolfrunner
|
| Revantusk Village, the Hinterlands
| Huntsman Markhor
|
| North-east of Frostwolf Keep, Alterac Valley
| Frostwolf Stable Master
|
| Thrallmar, Hellfire Peninsula
| Huntsman Torf Angerhoof
|
| Zabra'jin, Zangarmarsh
| Khalan
|
| Stonebreaker Hold, Terokkar Forest
| Trag
|
| Garadar, Nagrand
|  Wilda Bearmane
|
| Thunderlord Stronghold, Blade's Edge Mountains
| Lor
|
| Mok'Nathal Village, Blade's Edge Mountains
|  Ogrin
|
| Shadowmoon Village, Shadowmoon Valley
| Gedrah
|
| Warsong Hold, Borean Tundra
| Durkot Wolfbrother
|
| Bor'gorok Outpost, Borean Tundra
| Breka Wolfsister
|
| Taunka'le Village, Borean Tundra
|  Halona Stormwhisper
|
| Vengeance Landing, Howling Fjord
| Robert Clarke
|
| New Agamand, Howling Fjord
| Mary Darrow
|
| Camp Winterhoof, Howling Fjord
| Mahana Frosthoof
|
| Venomspite, Dragonblight
| Garmin Herzog
|
| Agmar's Hammer, Dragonblight
| Soar Hawkfury
|
| Conquest Hold, Grizzly Hills
| Craga Ironsting
|
| Venture Bay, Grizzly Hills
| Kor
|
| Camp Oneqwah, Grizzly Hills
|  Soulok Stormfury
|
| Camp Tunka'lo, the Storm Peaks
| Udoho Icerunner
|
Neutral stable masters
| Location | Stable Master
|
| Ratchet, the Barrens
|  Reggifuz
|
| Booty Bay, Stranglethorn Vale
| Grimestack
|
| Gadgetzan, Tanaris
| Laziphus
|
| Everlook, Winterspring
| Azzleby
|
| Cenarion Hold, Silithus
| Squire Leoren Mal'derath
|
| Cenarion Refuge, Zangarmarsh
| Kameel Longstride
|
| Area 52, Netherstorm
|  Liza Cutlerflix
|
| Scryer's Tier, Shattrath City
| Ilthuril
|
| Aldor Rise, Shattrath City
| Oruhe
|
| Skyguard Outpost, Blade's Edge Mountains
| Skyguard Stable Master
|
| Sun's Reach Harbor, Isle of Quel'Danas (Note: Spawns after Phase 4 capture of Sun's Reach Harbor)
| Seraphina Bloodheart
|
| Unu'pe, Borean Tundra
|  Trapper Saghani
|
| Kamagua, Howling Fjord
| Trapper Shesh
|
| Moa'ki Harbor, Dragonblight
| Trapper Tikaani
|
| Wyrmrest Temple, Dragonblight
| Risera
|
| Magical Menagerie, Dalaran
|  Tassia Whisperglen
|
| The Argent Stand, Zul'Drak
| Fala Softhoof
|
| Zim'Torga, Zul'Drak
|  Asgari
|
| Nesingwary Base Camp, Sholazar Basin
| Hadrius Harlowe
|
| K3, the Storm Peaks
| Heksi
|
| Brunnhildar Village, the Storm Peaks
|  Kari the Beastmaster*
|
| Bouldercrag's Refuge, the Storm Peaks
|  Andurg Slatechest
|
| Argent Tournament Grounds, Icecrown
| Thomas Partridge
|
| The Shadow Vault, Icecrown
|  Imhadria**
|
* Kari the Beastmaster turns friendly after completion of the quest [79] The Crone's Bargain
** Imhadria is only available after completion of the quest /
[80] If He Cannot Be Turned
[Worg Pup] – Quest Reward from 
[59D] Kibler's Exotic Pets can be restored if you destroyed the item but have finished the quest.
