Eternal Life is required for many crafted items for healers, especially later on in WotLK. Just like the other elemental ingredients in Wrath of the Lich King, it is created by combining 10 Crystallized Life.
Farming Eternal Life with Herbalism
Eternal Life can also be gathered from herbs using Herbalism. These herbs sometimes contain some Crystallized Life in addition to the herb:
Eternal Life Farming in Zul’Drak
The Mossy Rampagers in the central area of Zul’Drak have a very good drop chance of Crystallized Life. The great part about these mobs is that if you also have Herbalism, you harvest them after killing them, for an extra chance to get more Life.
Howling Fjord Eternal Life Farming
Similar to Zul’Drak, the Thornvine Creepers in the northern part of the Howling Fjord are the same type of creature. These mobs have a slightly lower drop rate, though they can also be harvested for an increased chance.