Primal farming in World of Warcraft is new to The Burning Crusade expansion. Its a great way to make solid steady gold to get that epic mount or new armor you might need. Obviously Throne of elements is the best place but it usually has lots of others there witch can slow down gains. Scald is usually a bit better and is the best spot for farming Primal Fire.
If you need Primal Manas Netherstorm is the place to go. Especially just outside of area 52. The mana wrathes and wyrms have good drop rates. Or the Mana Ghosts by kirin var village ruins. Primal Air can be found throughout Nagrand and in Shadowmoon valley. The Mobs that drop the motes are usually pretty spread out and hard to farm.
Nagrand Halaani basin is 1 of the best places to get Primal Water. The Mobs are low level and easy to farm. There is plenty of them and they are not immune to frost so its the perfect place for Frost mages to farm any Primal water they would need.
There is a lake at the Northern edge of Terrokar forest witch has a type of Mana fish that can drop Primal Manas. This used to be a good secret spot but it may have some competition there nowadays.
Primal earth and life should come from the Gathering profession.But if your server supports it you can farm the Bog lords north of swamp rat post in zangarmarsh for Primal life. And the various Earth elementals in Nagrand for Primal Earth. For Primal Shadow Farming the Void spawns in Nagrand or Hellfire.
Over all farming Primals is a solid way to make gold. Its easy and mindless. Try focusing on the Primals with good Auction House value on your server.