Dragon Flight

Free Routes:

Rousing Earth - The Waking Shore
Rousing Frost / Fire - The Waking Shore
Rousing Decay - The Azure Span
Rousing Air Farming - Ohn'ahran Plains

Battle For Azeroth

Free Routes:

RoyalJelly - Stormsong Valley

Cataclysm

Free Routes:

Volatile Fire - Mount Hyjal
Volatile Water - Twilight Highlands

Wrath of the Lich King

Free Routes:

Eternal Life - Howling Fjord
Eternal Fire - Storm Peaks
Eternal Water - Zul'Drak

The Burning Crusade

Free Routes:

Primal Fire - Hellfire Peninsula
Primal Shadow - Hellfire Peninsula
Primal Earth - Nagrand
Primal Mana - Netherstorm
Primal Air - Shadowmoon Valley

Vanilla

Free Routes:

Living Essence - Blasted Lands
Essence of Air - Silithus
Essence of Water - Swamp of Sorrows
Essence Of Undeath - Winterspring