ghost iron ore currently, people are lazy and now that ghost iron ore can be used to level from 1-600 BS people have been buying it up like crazy. Also trillium really well in single pieces.
I am not a hardcore gold farmer but I do save all my money and selling ore usually brings me about 15-20k a week. I send anything above my 10k limit over to my bank alt. this gets it out of my mind and if it is out of my mind I am not inclined to spend it which has allowed my little bank alt to amass quite a hefty sum of gold meaning as soon as I hit endgame in woD I will be able to get the enchants I need, buy the new dark moon trinket and still have enough gold to help my guild mates do the same lol.
Mind you as of tonight, WoD ore will replace pandaria ore and that will become my new money maker also the chance for a new pet from mining means a chance for a few extra thousand gold any time I go farming in WoD.