As some of you know, I run both this site, and MakeWoWGold.com, where I give free advice and strategies on making gold in the game.
Recently I went back through emails that I had received from MWG members and visitors and conducted a study on which published gold guide they found most helpful. I decided to do that because with all the feedback I'd gotten I detected a trend and wanted to verify it. Sure enough, there was one guide that everyone liked the most. So I did a review of it on MWG.
The long and the short of it is this: There's a guide called Gold Secrets that members raved about. It has a fantastic guarantee, and a ton of very useful bonuses. It is the total package of gold-making guides. He is even setting up private message forums for folks to share information about.
I try to give out as much information as I can for free on MakeWoWGold.com, but he goes into more detail than I have time to do. (Between tracking optimal mage strategies and gold-making strategies, I could make a full-time job of it!) So, I sincerely recommend his guide if you're going to go for one of the published ones out there.