I've been working the earthstorm diamond market for as long as my JC friend has had the recipes to cut them. I keep a large supply of the mats required on a bank alt, checking the AH once in a while for cheap primals and green gems. keep a stack each of those mats on my alchemy main. Every single day i make my diamond (hoping for mastery procs) and send them to the JC who does all the work from there. The actual price of the mats has fluctuated, and with 2.4 the primal prices have soared, but it still remains quite profitable. It helps that my JC is a real life friend, because there's some degree of trust when i don't keep track of anything. He tracks how many i've sent, and sells them on the AH after cutting, sending me back 90% of the return. He works the market well enough to not sell when prices are low (and they've gotten much lower on my server than Inaiwae, there have been streaks of weeks where relentless was going for 110-120g) Regardless, there's always at least a 20g profit to be made per gem. before S3 came out, we stockpiled the supply, and sold thousands upon thousands of gold worth of diamonds in the 2 days after release, at 250-300g per earthstorm.
I know the nether vortex belts have been mentioned, and this probably varies per server, but for some reason there are at least half a dozen people selling Belt of Blasting on my server, to the point where it's not profitable to bother crafting and selling them. I've found the Belt of Natural Power to sell VERY well though, at a cost of about 1200g for mats, and i've sold them for anywhere between 2100g and 3000g. I made about 20k gold on belts in my 2 month parental leave that happened to coincide with the release of 2.4.
