I'm always hesitant to post links to the various gold-making guides on the net, simply because manyt of them are on questionable sites, seem to lean towards straight-ahead farming, or if they are legitimate (i.e. don't advocate exploits or other shady behavior), still aren't really all that useful to the everyday player who wants to make gold legitimately as they play the game, not neccessarily to the exclusion of everything else. I have found a couple, however, that I think are pretty handy.
For beginning players, this guide posted recently over at societyofgamers is something I would have really liked to read when I was just starting out in WoW. It's very basic, and isn't anything a seasoned player wouldn't be able to tell you, but for newcomers to the game, it gives the basics of the major professions, the auction house, and other scources of income & gives a few helpful tips about each.
For more seasoned players, another handy guide is Cthulhu's Gold Making Guide, posted over at Allakhazam. It's semi-Horde-centric (that's a hyphen-hat-trick, by the way), but it has some really useful tips for specific areas & quests that will allow you to rack up some loot. I used this one a lot when I was leveling my first character.
Have any of you come across any useful guides or perhaps written your own? I'd ask readers to send in their tips, but nobody ever wants to give away their gold-making secrets. Lousy capitalism....