This is a question on a lot of minds right now; as the expansion (and patch 4.0.1) looms nearer, people stop raiding and PvPing seriously, and the markets for many types of goods dry up. People are more likely to figure that 4,000g will be more valuable to them in Cataclysm than an iLvl 264 epic will be. What to do?
For starters, there are a few changes that are coming in patch 4.0.1 that can make you money if you plan for them. Since the patch will bring us the new class and combat mechanics, a lot of players will want to completely regem their equipment. For example, all armor penetration gems are being turned into crit rating. Even if players stop raiding, they'll want to put something in there to replace what may not be the best thing to gem. Knowing this, Blizzard seems to have made transmutation of epic gems no longer incur a cooldown on the PTR. That's right -- assuming this makes it to the live realms, you will be able to produce raw epic gems with an alchemist for the cost of the eternal and blue gem.
This large increase in demand and supply will likely affect different servers differently, but I predict we're going to see the same thing we saw when Transmute: Titanium and Smelt Titansteel went off cooldown: a quick drop in price, but not to the cost of the mats before the patch went live. The mats will be incredibly inflated for a while, as people who discovered that the cooldown was taken off buy them all; eventually, the prices will settle down to slightly more than the mats. Additionally, this means that the blue-quality gems generated by your Saronite shuffle will now be highly sought-after for transmutation into epic gems. You can easily make money with jewelcrafting and alchemy after 4.0.1 by transmuting and cutting epic gems to take advantage of all the regemming that people will want to do.
Another jewelcrafting business that should hold up well is selling mats to people leveling their skill. The end of an expansion is a good time to finish up trade skills, and you might be able to make decent money by prospecting old world or Burning Crusade ore. Adamantite particularly seems to have a good profit margin on many realms. You can see whether this is the case by plugging in the average prices you see into wowprospector.com.
I wouldn't suggest getting into glyphs, especially not on a server like yours, because it's a good bet that there are already several people pushing prices downward. I suspect that inscription will keep its money-making potential in Cataclysm, but don't level the trade just to sell glyphs. There are quite a few profit centers offered by inscription, and selling glyphs into a mature market with plenty of competition puts you against some people who are willing to play for hours at little profit just to drive people away.
Also, if you're looking for a way to make money with your current trade skills, check whether there's something you can do with enchanting scrolls. People still buy them, and if you use the right production and selling mechanics, you won't be crafting the ones that are no longer profitable. Also, if you have any enchants that can be put onto BoA gear, those will continue to be in constant demand through the next expansion.
Maximize your profits with more advice from Gold Capped, plus the author's Call to Auction podcast. Do you have questions about selling, reselling and building your financial empire on the auction house? Basil is now taking questions for a special series, "Ask an auctioneer," at email@example.com.