I've spoken before about some of the game guides available out there but these 3 are way ahead of the others. Gold guides aren't for everyone, I understand that and yes, much of the information is available on the internet for free but you have to hunt it down! For busy people, a few dollars spent on a guide can save you a lot of time - it all depends on your own preferences of course!
I've used Zygor's for leveling since mid-Wrath and it really does speed things up for me. The Loremaster section made that achievement much easier too and there's separate guides for Horde & Alliance, one for profession help, achievements, mounts, pets - it's all there for you.
I've recently joined Marcus Ty as co-host on his podcast, the Journal of Marcus Ty. I've also been an affiliate for his guide for over a year & I've read it cover to cover. He has added some bonus guides too as the main Auction House Secrets section got too big! Well worth a read in my opinion
And last but not least, Cold's Mysterious Fortune Card guide - these are still selling very well on my server & I'm sure, if I followed Cold's instructions more closely, I'd be raking in the gold even quicker!