Now that the commodities markets are cooling and the Cataclysm expansion starts to shake off its fledgling exuberance, I've started to turn back to the Auction House to supplement my strategic gold reserve. A great source of potential profit is level 83-85'ish gear that is *not* crafted. In other words, world drop gear that doesn't compete with an affordable crafted item for a given slot.
Players tend to throw these items onto the auction house for a couple hundred gold when many of them are still able to be sold for a couple thousand gold. The margin won't be there forever, but many players are still in the process of leveling their characters, be them main or alternate, and to enable them to participate in the item-level dungeon requirements for the Random Dungeon tool, and just to get a firm footing with above-average gear, they are willing to pay well.
Also remember that there is a lot of new gold floating out there for those who found their niche to fill at the beginning of Cataclysm. This economy is not the same as it was a month ago, and prices are all over the board on a daily basis. Don't be afraid to let something sit at what may be a borderline outrageous price. You might be surprised when it sells.