Blacksmiths in Wrath of the Lich King could make some decent money, just by pulling Cobalt Ore/Bars off the auction house and heading to a forge. The two best income sources by this means continues to be profitable and shows no signs that things will stop.
The first method was to make Notched Cobalt War Axes. These one-handed axes can be made for 10 bars, and guarantee a profit. No, they aren’t a great weapon. They’re great for Enchanting materials, namely Greater Cosmic Essence. More often that not, DE’ing one of these will bring you two Greater Cosmic Essence in return. Without even looking at whether Lesser Cosmic Essence could make the move even more profitable, you’ve got a system that costs you less than 10g and on average yields 20g (Ore/Bar is less than 1g per, while the Greater Essence is usually around 10g each).
The other way to make some decent money was to create the level 70 Cobalt tanking armor pieces. Each piece tends to take 4-6 bars to make and brings back close to double that (or more in some cases). The reason is pretty simple: you can’t get that kind of tanking gear as a fresh 70. The Cobalt gear destroys any Outland green or blue someone might have as they come to Northrend and most people aren’t going to raid for epic gear when they can just keep leveling. They’ll instead take the Cobalt gear which better suits them for the 70 Dungeons. Just remember with the BoA slot items now, Shoulders and Chestpieces aren’t as popular as they were.
Despite a reduction in popularity, both of these methods continue to work. The reason I bring them up today is because I’m seeing a drastic drop in Cobalt units as of late. Both Ore and Bars have been in the 40-70 silver range, which becomes a license to forge gold by way of the two things mentioned today.