List of Rares by Zone

Eastern Kingdoms
(25-30) Arathi Highlands
(44-48) Badlands
(50-60) Blackrock Mountain
(55-60) Blasted Lands
(49-52) Burning Steppes
(30-35) Cape of Stranglethorn
(1-10)   Dun Morogh
(20-25) Duskwood
(40-45) Eastern Plaguelands
(1-10)   Elwynn Forest
(1-10)   Eversong Woods
(10-20) Ghostlands
(20-25) Hillsbrad Foothills
(30-35) Hinterlands
(10-20) Loch Modan
(25-30) Northern Stranglethorn Vale
(47-51) Searing Gorge
(10-20) Silverpine Forest
(1-90)   Stormwind City
(51-55) Swamp of Sorrows
(1-10)   Tirisfal Glades
(35-40) Western Plaguelands
(10-15) Westfall
(20-25) Wetlands

Kalimdor
(20-25) Ashenvale
(10-20) Azshara
(1-10)   Azuremyst Isle
(10-20) Darkshore
(30-40) Desolace
(1-10)   Durotar
(35-40) Dustwallow Marsh
(45-50) Felwood
(35-40) Feralas
(1-10)   Mulgore
(10-20) Northern Barrens
(55-60) Silithus
(30-35) Southern Barrens
(25-30) Stonetalon Mountains
(45-50) Tanaris
(1-10)   Teldrassil
(40-45) Thousand Needles
(50-55) Un'Goro Crater
(50-55) Winterspring

Outland
(65-70) Blade's Edge Mountains
(58-70) Hellfire Peninsula
(64-70) Nagrand
(66-70) Netherstorm
(67-70) Shadowmoon Valley
(62-70) Terokkar Forest
(60-63) Zangarmarsh 

Northrend
(70-72) Borean Tundra
(71-80) Dragonblight
(73-75) Grizzly Hills
(68-72) Howling Fjord
(77-80) Icecrown
(75-80) Sholazar Basin
(77-80) Storm Peaks
(73-77) Zul'Drak

Cataclysm Zones
(82-83) Deepholm
(85)      Molten Front
(80-82) Mount Hyjal
(84-85) Twilight Highlands
(83-84) Uldum
(80-82) Vashj'ir

Pandaria
(89-90) Dread Wastes
(90)      Isle of Giants
(90)      Isle of Thunder
(85-87) Jade Forest
(86-90) Krasarang Wilds
(87-89) Kun-Lai Summit
(88-89) Townlong Steppes
(90)      Vale of Eternal Blossoms
(86-88) Valley of the Four Winds

Full Continent of Pandaria Map: Rare Pandarian Champions by Type

Timeless Isle
(90)      Timeless Isle

Darkmoon Island
(1-90)   Darkmoon Faire

Draenor
Voidtalon of the Dark Star & Edge of Reality Spawn Locations
New Rares in Nagrand and Tannan Jungle (NEW Patch 6.2.2)
Yay mounts! The Seven Mount Dropping Rares of Draenor
(The links below will take you directly to the Wowhead Guides for each zone)
(90-93)   Frostfire Ridge
(90-93)   Shadowmoon Valley
(92-94)   Gorgrond
(94-96)   Talador
(96-98)   Spires of Arak
(98-100) Nagrand
(100)      Tanaan Jungle