If you’re leveling your first toon, or the first toon on a server, you’ll need to raise some gold for things like training, mounts, and glyphs. Here are a few items that are very easy to acquire that you can sell on the auction house for quick WoW gold.
Cloth: You can obtain cloth from humanoids. From questing and dungeons you will probably accumulate several stacks. Cloth is used for first aid, tailoring, and has various uses for other professions.
Meat: People who are power leveling cooking will buy up meat from the AH instead of farming it. Don’t make the mistake of selling your meat (or any other cooking mats) to a vendor!
Armor and Weapons: Green (and blue) Bind on Equip items that you acquire can either be disenchanted and the mats sold, or sold as-is. Selling armor and weapons on the AH will incur a higher deposit fee, so make sure to only list greens that will sell. Items with less useful stat combinations such as Strength/Spirit or Agility/Intellect are good candidates for disenchanting, while items with more useful stat combinations such as Strength/Stamina or Intellect/Spirit are more likely to sell.
Herbs, Ore, and Leather: Learning a gathering profession at the low levels will provide you with all of the gold you need while leveling. Additionally, herbalism and mining will help level you faster as you gain experience while gathering nodes.
Limited Quantity Vendor Items: Many vendors offer formulas, mats, and other items in limited supply at a very low cost relative to their worth. Some formulas can be flipped on the AH for many times what you pay at the vendor. Most enchanting supplies vendors will carry a few Strange Dust and Lesser Magic Essence for a few silver, and on most servers these can fetch at least 50 silver each!