I find the best way is to just do instances, both 5 man or 25 man. In 5 man instances on heroic difficulty you can make a lot of money on trash loot, high level greens, blues and disenchanted epic items if the item is not needed. I have made over 200G on one heroic run through Ramparts.
I also do a lot of blacksmithing with my warrior (axesmithing) and I regularly get orders for extremely hard to craft axes, as I have a constant supply of nethers regularly raiding SSC, Mag, Kara and Gruul. I have purchased an epic flying mount and two regular flying mounts for my alt characters with gold made just with this months crafting orders.
My rogue is max herb/alchemy and I regularly do runs around with him to brew a few potions. If I get lucky with elixer mastery I can make over 100g per herb run.
I can also imagine making a ton on rare enchants, thus I am levelling my mage to 70 so I can start to dabble in that market.