The Undermine Journal, have you heard of it? If not, I suggest you start using this awesome website right now. It's made me thousands upon thousands of gold in a matter of minutes.
What the site is, is basically a mobile Auction House. You can see the prices of items during the past two weeks, It will show you the prices of items on other servers, and it will even show you how often and at what time certain items are posted. This is an excellent resource that should be used daily, by everyone. Seeing that it's free, there is no reason not to be using this tool.
One of the best things about the site is that you're able to log in, and put notifications on items, so when they pop up at the Auction House, you get e-mailed instantly. This is an excellent way to watch out for those rare recipes. So far, I've been able to snag 20+ rare recipes all for under 500g total. Schematic: Arcane Bomb, Schematic Lifelike Mechanical Toad, Enchant Chest: Greater Stats, are some to name a few.
I will show you how to properly set up notifications so you can receive e-mail alerts.
Not many people notice the top left hand corner of the website, you can create an account here. You can sign in with many different accounts, from Gmail, Twitter, Blogger, Facebook, and many more. Create an account and input your e-mail and have it verified. The whole process takes under 2 minutes.
Once you're signed up, find your server. Please do note that at the current time not all realms are supported and there is only support for the US, no EU support. Once you've found your server and faction you're ready to start setting up notifications. Type in the name of some rare patterns into the search box, and scroll down about half way down the page, you'll see Market Notifications for [Name], such as the image below.
After you've set your notifications, you will get an e-mail alert every time an item is posted below your threshold. The e-mail looks like the image below, it tells you how many are posted, and at what price.
But that's not all!
It sounds like an infomercial, I know, sorry. But seriously, that's not all the site can be used for. You can also have the site scan through your professions and tell you what items are best to craft, which items are going to yield you the best profit. This is especially useful on professions such as Enchanting, Blacksmithing, Leatherworking and such. If you're a gatherer, you can see which herbs are yielding the best gold, this way you know what herbs or ores to go out and farm.
You can even track the top sellers on your realm, see what they're posting and at what times. This is simply amazing, you can basically monitor your competition 24 hours a day, 7 days a week without even being online!
Please do keep in mind that the prices that The Undermine Journal can sometimes be wrong. There are sometimes outliers that make the value some items incorrect. This isn't a sure-fire way to check prices on items, but rather compare them to what other people on other servers have them posted on.
By not using this excellent resource, you're only gimping yourself of those thousands upon thousands of gold, so what are you waiting for!?