World of Warcraft requires a great amount of gold in order to have the best experience, so it's very important to know the high yield gold farming locations. Even if you're not buying the latest and greatest sets of armor and weaponry, you'll want the gold for buying the next mount upgrade, an enchant, gems, potions, or simply for just travelling all over the world. It doesn't feel great to be one of the world's great heros and yet have the world's smallest wallet.
Luckily, this can be easily solved. Almost everywhere you go you can farm valuable materials that you can sell for a tidy profit on the auction house. The auction house will take care of your products' sale on your behalf, and will actually mail you your winnings. You don't even have to pick up the gold. And if your materials don't sell, you can just put them up for auction again for a lower minimum price and you hardly lose anything from the attempt. Always auction off your materials.
With the introduction of World of Warcraft: Cataclysm, the entire world was changed, including gold farming locations that players had become used to over many years of playing the game. Old mining locations or herb-picking zones have changed dramatically, while previously desolate zones which offered nothing of worth have suddenly become fantastic gold farming locations that nobody has ever tried before. Opportunity is there -- your character just has to take it.
Cataclysm also introduced some entirely new zones with all-new high-level materials needed for most high-level recipes. People will need and want these materials -- unfortunately, they're incredibly rare. You have to go out of your way to find them.
These materials are the Volatile elements. Volatile Fire can most easily be found in the Twilight Highlands. You can loot them by simply killing Enslaved Infernos, but more easily you can get them from fishing at a place called the Pool of Fire. Even if your fishing skill is at a measly 1, you'll get Volatile Fire out of it easily. This makes the Twilight Highlands one of several great gold farming locations.
The best of all the gold farming locations for Volatile Air is Uldum. Kill off all the Scions of Al'Akir, which are large in number and quick in respawn rate. They drop Volatile Air at a good rate and you can then take that to the auction house and sell them at a tidy profit.
There are two good gold farming locations for Volatile Earth. One is, again, in the Twilight Highlands. Find Obsidian Stoneslaves and kill them off as they respawn and they'll drop some. Meanwhile, Mount Hyjal has Scalding Rock Elementals that respawn quickly and are easy to kill en masse, and they'll drop Volatile Earth as well.
Finally, some good gold farming locations for Volatile Water. The best spot is, once again, in the Twilight Highlands. Go kill off Muddied Water Elementals. If you are already leveling up your fishing profession, go to any fishing node in the new Cataclysm zones and you can fish Volatile Water from there, too.
There are plenty of good gold farming locations throughout the game, but the Twilight Highlands has a lot of them. That may make them overcrowded so try going to others if you see other people farming your gold farming locations.
However to optimize your gold farming rate, you definitely want to use a WoW Gold Addon that will guide you to the high yield, low competition farming areas. However farming is probably one of the slowest methods to make gold in WoW. The Addon I use helps you maximize gold potential in farming, gathering, crafting, and playing the auction house.