Enchanting - Making Gold by Disenchanting.

This may seem another obvious thing, but for any enchanters out there, anything green or above, Disenchant it! Disenchanting Items can provide huge amounts of gold, and the best thing is that since disenchanting is bundled with enchanting you don't need to waste a trade skill like you do with herbalism and mining.

You may find enchanting materials can make huge amounts of gold in WoW, like Dream Dust and Vision dust sell which extremely well. When you hit the outlands Arcane dust, Greater Planer Essence and Large Prismatic Shards are also worth quite a nice sum.

You will find Large Prismatic Shards are the best money makers and come from blue instance items in the outlands. The best place to grind these is in some of the higher end instances in the Outlands, to do this you will need a group, and share the Large Prismatic Shards, but on the plus side on the easier instances you can get through them quite quickly and Large Prismatic Shards do sell for a lot of gold, even after the introduction of Void Shatter in Patch 2.4 which has a 24 hour cooldown.

Ontop of these though there are many different kinds of enchanting materials that sell for a lot of gold in WoW, making disenchanting a very profitable way to make money on the auction house!