Enchanting

Well, specifically disenchanting can make some easy gold without ever leaving the AH. It works best on established servers, the older the better. Don't worry if this isn't a chosen tradeskill, just roll another character, get him (or her) to level 5 and get enchanting as a skill. Mail your new character a couple of gold to get started.

Look in the AH for green armor, it doesn't matter if it is cloth, leather or anything else. To start with look for items for level 16 or 17. These will disenchant into either Strange Dust (77% chance, up to 5) or Lesser Astral Essence (14% chance, 1 or 2) or Small Glimering Shard (rare). Check the price of these enchants in the AH and base your bid for the 16 or 17 items on the selling price of the enchants.

These are some examples taken from one server:

Strange Dust sells around 6 silver. Lesser Astral Essence sells for 30s.

Given these prices, the average disenchant value is about 23 silver. In practice, the quantities obtained are a bit higher, giving a disenchant value of 30 silver.

Bid or buyout anything less that 15 silver. Disenchant the armor and add the enchants to the AH for a 100% average profit.

Repeat and double your gold each time.

Once you have 10 gold or so, you can move onto higher level items.