I find this works best on a Druid, however it is still very simple and easy to do with any class.
Simply check the daily "Troll Patrol" in Zul'Drak for the Daily "Can you Dig it?" to come up. You are given a pick and sent to go dig piles of dirt nearby. There is a 1/3 chance on digging with the pick to get a box, and inside each box is a small amount of silver and items, and 100% drop on a grey worth 3g each to the vendor.
The other 2/3 of the time a mob will spawn, either a Troll or a Spider, if you leave combat with the spiders they will de-spawn, however the trolls will not, so if you have a vanish ability it can save you a bit of time, though the mobs die easily enough anyway.
You can continue to dig after the quest is complete as long as you don't turn it in, and the piles of dirt are all clumped in a very small area. If you are a druid, you can use the pick and use Flight Form before a mob spawns to avoid combat entirely and continue on to the next dirt pile.
I generally can pull in about 300g/hr with this method as a druid, more or less depending on your luck. Its a nice way to kill time between queues and make some cash fairly effortlessly though.