Cobra Scales are needed by high level Leatherworkers to make many high level equipment such as Cobrascale Gloves. Now just one of them can go up to 30G, think how much money you can make with a stack of them…
These Cobra Scales are dropped by many mobs, the ones that are killed the easiest are the Coilskar Cobras in Coilskar Cistern, Shadowmoon Valley. Now obviously the drop
rate for the scales are extremely low (0.1% according to thottbot) but the good thing is that there are a lot of them around. There is a cave at Coilska Cistern which has quite a few of Coilskar Cobras. With a good level 70, you can get 3-4 scales an hour – thats 90-120G an hour! You also get a pile of Green items which can add another 10-20G 
Note: As before, this is a high level grinding spot. I recommend you to be level 70 to farm here. Get the Team iDemise 1-70 Leveling Guide if you are still not level 70 yet. I guarantee you to hit 70 within a weeks game time whether you are level 60 or level 8! I have personally used this guide and use it everytime without fail when i reroll on different servers. It’s worth the small price