A player by the name of Kunzite recently submitted to us that he had released his gold-making guide, subtitled "How I Made 100,000 Gold." With a title like that, I had to check it out, and it has some very interesting tips in it. It is extremely long, which makes it all the more surprising that it's free. A lot of the tips are along the lines of playing the auction house, but there are also some helpful introductions to concepts like opportunity cost (a vital thing to wrap your head around in WoW), and detailed lists of what crafts you can turn a profit in (if only by disenchanting them), and so on.
I know I'll be coming back to this site – I haven't read it all yet, but it is a very nice resource, and who couldn't use a little more gold? I've already implemented one of his suggestions and found it to be quite lucrative: farming for Fel Armaments and Marks of Sargeras from warlocks at Legion Hold. My previous go-to gold-making strategy (fishing in Nagrand) was getting me 200-300g an hour typically; Legion Hold would be more like 400g if I sold everything, and I need the Aldor rep anyway (so I'm selling the Armaments and turning in the Marks). The best part about Legion Hold is that the mobs there are perma-spawned: there are always at least certain number alive at a time, so no matter how many people are farming there, you never have to wait for spawns.
Kunzite's guide, like Jame's killer leveling guides (Alliance, Horde), is astonishingly high-quality – and completely free! Go check it out if you have any interest in better ways to make gold. And to Kunzite, thank you for making this great resource available to the community.