Rune Thread

If you want to make money doing barely anything then this method is for you. It can over make 40g a day and only takes about 5 minutes. The downside is that it only works well on some realms and requieres you to have about 10g to start you off.

The trick is to buy Rune Thread for 50 silver off any Trade Supplies vendor, they are in unlimited supply. They can then be sold at Auction House for 1.5g each and sometimes up to 8g or so! You'd think that people don't buy them but often people do (at least on my realm).

I presume it's mostly non-tailors who are getting the mats for an item (its used to make over 200 different items) and just buy everything at the auction house, for this reason I usually put them in stacks of 5 or 10 since people don't usually need more.

Also make sure that you're selling them cheaper than everyone else and don't put in more than 20 a day, because they can sell off any vendor Trade Supplies vendor the demand isn't very high so its unlikely that more than that will sell (remember that high supply and low demand makes the price drop).

Farming Motes/Primals

This method involves killing a type of enemy over and over again for motes, that can be changed into primals, these are: Mote of Water, Mote of Shadow, Mote of Life, Mote of Fire, Mote of Mana, Mote of Air and Mote of Earth.

Here are the locations:

Mote of Life
[Zangarmarsh][60-61][Withered Giants][Best]
[Zangarmarsh][62-64][Starving Fungal Giants]

Mote of Water
[Terokkar][62-64][Shimmering Eels][Best]
[Nagrand][64-66][Lake Spirit]
[Nagrang][65-67][Lake Surger]
[Shadowmoon][67-69][Enraged Water Spirit]

Mote of Fire
[Blade's Edge][66-68][Searing Elemental][Best]
[Shadowmoon][68-70][Enraged Fire Spirit]

Mote of Air
[Nagrand][65-66][Storm Ripper]
[Nagrand][66-67][Living Cyclones][Best]
[Netherstorm][68-70][Enraged Air Spirit]

Mote of Earth
[Nagrand][64-65][Tortued Earth Spirit]
[Nagrand][65-66][Enraged Crusher][Best]
[Shadowmoon][67-69][Enraged Earth Spirit]

Mote of Shadow
[Nagrand][65-66][Voidspawn] [Best]
[Netherstorm][68-69][Voidshrieker]
[Netherstorm][68-69][Unstable Voidwraith]

As you can see most of the best locations are in Nagrand, so if you have an epic flying mount it's a pretty good idea to fly about and get some of each. If you don't then the Motes of Fires are the best (however you aren't level 70 then go for the Mote of Water).

The prices at the Auction House vary depending on the Primal and then realm but most of the time Primal Fire is the most expensive and Primal Shadow the least.

Credit goes to WoW Tips for some of the locations.

Deviate Fish

One very simple way to make gold that will work great at level 30 and over is to fish Deviate Fish. For this to work you must have 150 Fishing and level 25. Find Fish and a mount will also help. These rare fish that sell for about 1g at Auction House can be fished anywhere in the The Barrens.

I've made a map with the best spots, The Forgotten Pools at X has a lot of pools and fairly frequent to get fish in open water.

The Wailing Caverns (Moon) is inside an instance, it has high chance in open water but no pools, its best on PvP servers since enemy players can't reach you there.

Outside the Wailing Caverns (Square) there is a few pools and a decent chance in open water.

My favorite is The Forgotten Pools but if you're on PvP and you're low level then go for the Waling Caverns. The best way to fish them is to find pools with Find Fish or by diving into the water and looking for them, and then fishing in the pools. If there are no pools then either fish in normal water or if you have a mount go to another fishing spot.

Remember that the pools give Deviate Fish 100% of the time while the normal water only about 30% (depending on where you fish) of the time.