On my server, there are people who place the buyout of the darkmoon cards (lunacy, blessings, etc) for the normal amount, but forget entirely about the bid which I've found on several so far to be only a 1g bid.
So during your AHing, just do a quick search for all 4 of the main cards (Storms, Lunacy, Blessings, and Furies) and skim them over.
Any and all that have a bid for 1g, place a bid. You've got nothing to lose, and if you win the card you can either resell it for roughly 10-40g (more on some server) profit or just save it for a deck and resell the deck for a HUGE income.
This is roughly common sense, but simply exploit people's carelessness. I've gotten quite a few cards this way and made a good amount so far from it.