If you really want to make gold, the absolute top method is going to be server & faction arbitrage.

Basically check out the Undermine Journal.
You're looking for something that sells for both a higher price and a higher volume on one server/faction and sells for a lower price but still high volume on another server/faction.

Once you find that...
Transfer a toon with gold to the buying server and/or faction.
Buy a bunch of them, as much as you can afford.

Transfer to the selling server and/or faction.
And unload them over several days.

You could go with more than one mule character.

This is essentially Blizzard legal, purchasing gold with real money.
Similar to buying the mounts/pets and then selling in game.