Traveler's backpack sells for A LOT. Usually, the Alliance realm is two or even three times more populated than the Hordes. To start, have your main character on the Horde side because that'll be the character in which will be receiving all the WoW gold. You'll need to farm a little gold for your Alliance character. When you've collected about 20 gold pieces go to the nearst Auction house and buy a Traveler's bag. Then fly to Tanaris and set your buyout price very low.

Now log onto your main character and buyout those bags. Be sure to do it quick so no one else grabs it before you do. Since the Alliance population is much bigger, there are much more bags available in the Auction House and the normally cost cheaper. If you sell them on the Horde side you will get a lot more for what its worth. A bag goes for around 5 gold pieces on Alliance and sells for 10 gold pieces on Horde. That's 100% profit right there.

Normally I would transfer over around 4 bags each time. That would be about 20 gold. Within a week I can farm about 4,000 gold pieces. That is a pretty decent amount even with the auction house taking about 15% on fees.

There are some recipes that sells for a great amount of gold. Best sellers are "Brothers Knaz" and "Gnaz Blunderflames" in STV. They sell Schematic: Deadly Scope and Schematic: Mechanical Dragonling. You can only buy one of each per day. Mechanical Dragonling costs one gold each which can easily sell for six gold. Deadly Scope costs 20 silver and sells for about 5 gold pieces. Another nice receipe is the Mithril Mechanical Dragonling, sold by Ruppo Zipcoil in Hinterlands. Costs 40 silver to buy and sells easily for 5 gold. I can on average about 100 gold per week running these small errands. It isn't very high income unlike selling Traveler's bags but it's a quick method with an extremely high profit margin.