It seems there has been a number of threads lately about how Jewelcrafting is a "dead" profession that is no longer profitable, how the gem market is crashed and gems are only selling for next to nothing.
I'm sorry, but if you think this, you are wrong.
Here's how I'm making bank with JC at the moment:
1) 450 JC rings/necklaces
Unbeknownst to many WoW players, there is a little lady in Jade Forest that sells JC recipes unknown by all the other JC trainers. Her name is Mai the Jade Shaper found at Greenstone Village just north of Dawn's Blossom. She teaches a set of recipes to make ilvl 450 rings and necklaces. Any freshly dinged level 90 character is searching the AH for quick and cheap gear upgrades and this is a popular one.
While the profitability in this area has gone down significantly since release, it is still very profitable. The limiting factor here is [Serpent's Eye], so check the AH regularly for when they go cheap.
2) Perfect cuts
Probably the biggest area I see people passing by is what to do with the leftover uncommon gems from prospecting. We all know they can be made into jewelry and disenchanted. But how many of us are already sitting on a mountain of dust and essences? But take a quick look at your AH, some people don't know what to do with them and are dumping them on the AH for dirt cheap. I'm betting you can find at least one color of uncut uncommon MoP gems that is selling for less than 3-4g each. I regularly find them on my realm for less than 1g each.
Take a look at TUJ's JC page for my realm about red gems:
The first row shows how much the uncut uncommon ([Pandarian Garnet]) and rare ([Primordial Ruby]) gems are priced, 3g and 122g respectively. The second and third columns show how much the perfect ([Perfect Brilliant Pandarian Garnet]) and cut ([Brilliant Primordial Ruby]) rares are priced, 204g and 173g respectively.
It has been reported on these forums many times, but a lot of people still don't recognize that the stats on a perfect cut are the same as on the rare cut (look at the perfect and rare brilliant cuts I just linked above).
So this is what I do. I'm buying up stacks of uncommon gems and cutting them. It's a 10% proc rate to get a perfect version, so figure that your cost for each perfect cut is 10x what you bought it for off the AH. In this example my cost for a perfect cut is 30g (10 x 3g). Post these up on the AH below either the perfect or rare cut price (in this case if I was doing Brilliant gems it would be at ~170) and you're looking at a nice hefty profit of 140g.
Wait, it gets even better. As I mentioned, I can often find uncommon gems in some colors for less than 1g. After cutting hundreds of uncommons, you'll be left with stacks of cut uncommons that weren't perfect. These vendor for 85s. So let's imagine I buy 50 uncut uncommons at 1g a piece. I cut them and proc probably 5 perfects. I can vendor the other 45 at 85s each and recoup 38g25s of that initial 50g investment. So my total cost for the 5 perfect gems is 11.75g or 2g35s each. Slap those up on the AH for a nice hefty profit.