This patch has been a windfall for gold-seeking professionals for a few reasons, but there have been some changes that affect everyone, no matter what addons you use or how much time you spend in the auction house. Let's start with the more subtle changes.
What's the most annoying part about mining and herbing? Unlike skinning, which simply lets you gather from a large number of creatures you are killing anyway, mining and herbalism force you to go out of your way to gather. Before patch 4.0.1, you could only track one thing at a time. Now, you can track everything at the same time!
This will make hunters and achievement seekers very happy. Anyone who wants to use tracking for more than either herbs or minerals can now just pick from a list of stuff they can see. Importantly, this makes double-gatherers much more viable than they used to be. People would typically only take either mining or herbalism because switching between them was a chore, and you could only track one at a time. Maybe that's why there are so many skinners? Now that you can track both at the same time, double-gathering is definitely the best way to make money with a trade skill while leveling.
How does this change your life now? Well, Cataclysm is expected to have two major developments for gatherers. First, while the auctioneer crowd will be trying to race to server-first skill cap on whatever they think will be the most money, people who farm ore and herbs will be making far more money until those crafting skills start paying dividends. Second, all the new goblins and worgen will need old-world materials to level their chosen professions. Farming for either of these sources of demand should be very lucrative. You don't have to wait until Cataclysm to farm for people leveling trade skills, either. None of the major raw base materials are changing, from what we know.
Of course, Hallow's End
Hallow's End just started, and like many holidays, contains plenty of ways to make some fairly easy gold. You can collect wands and charge "tips" for people looking to get the achievement, and you can sell a bunch of random items on the auction house like the Weighted Jack-o'-Lantern.
One of the changes this year is that people hoping to save 5,000 gold for the 310 percent flying skill will all want to get What A Long Strange Trip It's Been. This means they need to do Check Your Head and The Masquerade, and generally, there should be more demand for the tradable holiday goods.
If you have a character high enough to solo ZG, you can make tons of money selling bijous and other rep items to people desperate to get the achievement before it gets removed from the game. There was a blue post that mentioned that while the Tome of Polymorph: Turtle would still be available after the expansion, but there's been no indication of how hard it will be to get. If you're too low a level to be able to solo ZG, consider going with a few friends and splitting the rewards.
No scribe? No jewelcrafter? No problem
The biggest demand right now is from people regemming and learning all their glyphs. If you aren't in a position to craft to serve this demand, you can still participate in the market. If you have money to invest, you can try buying cut or raw gems when there's a lot of supply and the prices are low and sell them on the weekends when there might be more buyers around than there is supply. Additionally, the Glyph of Mage Armor can't be made anymore because of a bug introduced in patch 4.0.1. If you can find it for less than 100g, you might be able to resell it for a profit. Since glyphs in general seem to be priced fairly low at the moment, I wouldn't speculate on buying and selling them yet.
Of course, there's always the old standby of selling Vanishing Powder at obnoxious markups. At least on my realm, however, people have happily caught on to this scam, and there's always tons of stock at what's getting really close to the price the vendor charges. If you want to sell vendor objects to players, at least pick something that saves them some travel time like old world mid level vendors.
Insider Trader takes you behind the scenes of the bustling subculture of professional craftsmen, examining the profitable, the tragically lacking and the methods behind the madness.