Not really an exploit, but i didnt know where to put this, and it's definitely something that can make you a ton of gold.
According to Censored 3.1 patchnotes, Black Diamonds will now be able to be used by jewlcrafters to create random gems.
Black diamonds range from anywhere between a few copper to 25s on my server. You can bet your ass they're going to be going anywhere between 1-5 gold a pop when that patch hits.
I did this with jagal pearls, herbs before wotlk, baelogs shortbows before it was blue, gloves of the fang, and several other items to make myself an obscene profit in the past. I figured I'd share this "little gem" this time around, since the profit margin will be so huge on these. =)