If there aren't any good profit opportunities, just go with what the market is selling at, or buyout everything of a certain cut and relist at a higher price. This is a very common practice on some servers, and we've seen friends that control entire gem markets because they're so stinking rich.
Note that you don't prospect for a fee. The gems those people get will be used to undercut your auctions, and since they're not in it for the long haul, they ultimately bring the market down because they don't undercut responsibly. All it takes are 3 or 4 of those guys, and the whole market for a gem or cut shifts down some gold.
Enchanting is pretty much entirely based on rare recipes for gold making. A good amount of gold also comes from disenchanting. If you're just starting out and in need of gold, go hit up the old instances and disenchant all the loot. There's still a huge market out there for people who want to hit max enchanting skill in a day or two. That old dust still sells well. Most essences are hit and miss, in addition to Magic Essence. It's used in the beastslaying enchant and still gets a few gold a piece for all those alts who want a glow on their new weapon. You can do like with the Alchemy profession once you get a comfortable amount of gold.
Checking the price of Large Prismatic Shards and Large Brilliant Shards is also not a bad idea. Once you get a good idea of the price, hit up the AH and buyout any 65+ blue that is below the buyout price of a LPS, and any 50-60 blue that is below the buyout price of a LBS. Unlike putting up other gear for auction, enchanting mats have no deposit, so you're not eating a loss if your mats don't sell.
Finally, if you're in the market purely for disenchanting and selling mats, don't disenchant other's items for free. Even a fee if you can avoid it. As per the JCer, most people without your profession undercut by a lot. It screws you in the end.Alchemy is unlike other professions, you don't need rare recipes to make world of warcraft gold. There are four potions, like Super Healing Potion, Super Mana Potion, Major Healing Potion and Major Mana Potion, which bring in major cash.
Tailoring serves two purposes: one is crafting and the other is specialty cloth. Unluckily, Tailoring requires a few rare patterns. Without selling the specialty cloth, it's a very nice profit for a quick craft on tailors every four days. For Horde, it's worthwhile to pick up the Robes of Arcana pattern. With everyone believing Warlocks are the be-all/end-all of OP'd solo ability, there are tons of alts that want to pick this item up to make their Bloodrobe.
Specialty cloth is also a decent gold maker, especially when you specialize. We pull in two primal mooncloth and two spellcloth every four days for the price of mats for one. Check the AH before you go crafting. If the value is way down, craft but don't sell until later. If there are none, craft and put up the cloth at a huge mark up. There's almost always that one person looking to craft that piece of gear tonight and will pay 20 g over the regular price to do it. 
Jewel-crafting also requires some rare recipes but even without it, you can make some decent gold. We used to farm adamantite /fel iron to prospect, but now we just buy it. In fact, we prospect all our ore and open up our JC profession window and checkmark "Have materials". We head over to the Auction House and then check which gem cuts have the largest profit or the one there are few or none of on the AH. We make 5 of each jewel based on 1/2, until all our gems are gone.