First of all, i want to say that this method can either be very profitable if your server supports it (like mine).
FIRST
You have to make some AH data gathering. Check the prices of [Arctic Fur] (75+ gold on my realm) and the prices of Heavy Borean Leather (50G per stack of 20 in my realm).
SECOND
You have to know, that there is leatherworking NPC (even tho its mostly known by leatherworkers) called Braeg Stoutbeard in front of the Dalaran's Leatherworking shop. He offers 1 Arctic Fur for 10 Heavy Borean Leather. Lets do the math.
20 Heavy Borean Leather = 50 gold
2 Arctic Furs = 20 Heavy Borean Leather
If the AH price for Arctic Fur is 75 gold you get clean profit of: (75*2)-50=100 gold.
And thats just for Buying / Changing the leathers into furs and reselling them.
The search for Arctic Fur is always high, they're used in all kind of Leg Enchants for melees and all kind of epic Leatherworking patterns for Leather/Mail wearers of lvl 80.
There are few more hints that can help boost your income.
If you're leatherworker: Check also the prices of Borean Leather. In some cases it is more profitable to buy normal Borean Leathers and make them into Heavy Borean Leathers yourself. I've managed to make Stack of 20 Heavy Borean Leather for the price of ~35 gold.
Darkmoon Fair is coming soon?: I strongly recommend placing a bank character in there with around 50G in his bag. Find the orc NPC named "Lhara" 
She sells Arctic Furs for 12 gold only. Also in stock there are Frost Lotuses, which go ~25-30 gold in the AH (the npc sells them for 4g). The problem there is that these items are with limited supply. The resupply time of these furs/lotuses has been reported to be 15-18 minutes, but it is not entirely sure. Other ppl claim that it took them 2 hours to resupply. Personaly i just check it from time to time during night and hit some arctic furs.
Good luck with the guide, i hope that it will help you boost your goldz =)