This really isn't all difficult and is rather easy:
Right inside AQ40 are 4 giant mobs. If you kill one of them you will be able to mine a large obsidian chunk right outside the of the instance. Kill three of the four mobs and run out of the instance and there will be 3 mines that will appear. Just be sure that you don't kill all 4 mobs and you will be able to repeat this as many times as you want. The large obsidian chunks sell for 100 to 300 gold on the auction house. So you can make 400 to 600 gold an hour doing this.
I've tryed this works well, and is 100% legit, try not to flame, thats all I've gotten out of my posts so far, more guides + exploits to come.
Enjoy,
- Ajuma