Ok, I know that some people have posted already about using 2 eternal earth to make a Stoneguard band, then DE'ing it and selling the materials, but i've got a way to make even more money than that (I believe). I've earned approximately 10k over the past week or so doing this, and obviously it depends on your server's economics, so you'll have to look for yourself.
Prerequisites: an enchanter with 325 skill
a Jewelcrafter with 380 skill and the following recipes:
Bloodstone Band - Thottbot: World of Warcraft
Sun Rock Ring - Thottbot: World of Warcraft
Crystal Citrine Necklace - Thottbot: World of Warcraft
Crystal Chalcedony Amulet - Thottbot: World of Warcraft
Economics on my server
To give you an idea of the money:
A stack of Saronite Ore on my server is going for about 35-40g (cheaper than Cobalt)
A stack of Infinite dust sells for approximately 100g (5g each)
Each lesser cosmic essence sells for about 10g
Each Eternal Earth sells for about 8g
So I'll go and buy up approximately 10 stacks of Saronite Ore. Spend no more than 400g. I'll prospect the ore, and each stack should produce 4-6 green gems and 1 blue gem.
That will net me approximately 50 green gems and 10 blue gems.
I will go and sell the blue gems on the AH, or if I've been doing the jewelcrafting dailies and I know recipes for the blue gems that sell for more than the gems themselves, i'll convert them. Usually Bold Scarlet Ruby and Delicate Scarlet Ruby sell for about 100g on my server. Worst selling Blue Gem is the Sky Sapphire, which sells for about 20g.
In general, I can make more than the cost of the Saronite ore just on selling the blue gems. I no longer bother trying to make anything out of the green gems because they don't really sell. But...
1. Sell all Shadow Crystals for whatever you can get for them. (usually 1-2g each)
2. Sell all dark jade for whatever you can get for them. (usually 1-2g each)
3. Assuming the law of averages, from your 50 greens, you should have about 33 or so left (Orange, Yellow, Blue, Red). Now buy 7 Eternal Earth (on my server, cost is about 56g for the 7). Convert them into Crystallized Earth.
4. Now take the left over greens and crystallized earth. combine 2 earths and one green crystal using the recipes above. Make Bloodstone Bands (red), Crystal Chalcedony Amulets (blue), Crystal Citrine Necklaces (orange), Sun Rock Rings (yellow). When you're done, you should have 33 rings.
5. Now DE them (or mail them to your enchanter to DE them).
Each ring/necklace yields 1-2 dusts (75%) or 1-2 lesser cosmic essences(20%) (and a small percentage 5% give small dream shards). Assuming these stats, your 33 rings should yield about 10 lesser cosmic essences and 37 dusts.
At the rates I listed above, that will be 10*10 + 37*5 = 285g.
So: Assuming you break even on the blues (I usually make a pretty good profit on them though), and you only sell the DE'd items, you get 285-56 = 229g per 10 stacks of Saronite. Takes about 15 minutes to do this.
Now do it 4 times in a day, and poof, 1000g (at least) in 1 hour of work.
Let me know if I got any of the math wrong. This has been working and making me a ton of money over the last week or so.