Alchemy is one of the most underutilized professions in World of Warcraft. Since this is the case, it’s easy to find ways to make some gold with it. While I’ve used all three masteries at one point, the most lucrative has turned out to be the Master of Transmutation. Transmuting Diamonds can be especially profitable depending on when you play and when you try to sell your wares at the AH. Another key to making gold with Alchemy is to buy the mats you need when their prices are low and then sell the finished product when the prices for those are high. Simple concept, but one that a player must always keep in mind when farming gold in World of Warcraft.
For more great tips on making gold in WoW with Alchemy and other professions, check out the WoW Secret Gold Guide.