I looked at all of the profession leveling guides at the two most popular sites, Almost Gaming; and Wow Professions, as these guides are what a lot of people will be using to level. The trick here is to anticipate what the customer will be buying, and what we can make a good profit on. We'll want to look for items that aren't easily farmable, or that are needed in such quantity that a leveling character just won't have accumulated enough and will need to turn to the AH.
- The first step is to look for basic materials. Some are difficult to farm, and some are just needed in such large amounts that a leveling character won't have enough and will need to buy the extra on the AH. Most old-world ore and herbs have plummeted in price, though, so those are out. As mentioned in my last post, Outland materials are a great place to start. Northrend materials are also good, especially cobalt (as saronite is mainly for high-level recipes, but Cataclysm recipes will be accessible at 425 skill). Netherweave and Frostweave Cloth are needed by tailors in massive quantities, and you can always make bags out of them if you can't sell the cloth. Thick, rugged, and borean leather should sell well to leatherworkers, because the quantities needed compared to the leveling speed at those points means they probably won't get enough on their own.
- The second step is looking at rare items. There are fewer of these, but because they aren't easily farmed, they can command high margins. These are all niche markets, so you shouldn't stockpile huge amounts, but carrying a small quantity of these can be profitable. These are things like crystallized air for blacksmiths, some of the various gems for jewelcrafters (citrines, huge emeralds, and blue sapphires should sell well), and black pearls and primal might for enchanters. Many of these are small markets that can be dominated by one player, so while volume may not be high, profits will be.
- The final step in making money off of profession levelers is BoE recipes. Guides often refer to BoE recipes as ways to save mats and be more efficient while leveling. Blacksmiths are told to buy the plans for Mithril Scale Bracers and Mithril Spurs (though the lower price of mithril might cause some to not bother), Pendant of the Agate Shield for jewelcrafters, etc. The formula for Enchant Bracer - Greater Stamina should be especially valuable, as enchanting mats are going up in price, not down.
An important point is that Cataclysm is going to introduce multi-point skill gains. This will change the most efficient leveling path for most professions, so some of the individual items named here might not continue to be profitable, but the overall strategy of understanding how a profession is leveled and what people will buy will still make you money.