You must equip your character with as much Golf Find and Pickup Radius gear as possible.
Also, you must be level 60. This is so you can take advantage of the Nephalem Valor buff. This buff happens when you kill elite packs. It provides a 15% bonus to Gold Find, and it can stack up to 5 times, allowing a total of 75% Gold Find increase.
You can do this in any area with elite packs, but there is atleast one particular area recommended. In Act 3, the Siegebreaker quest. This quest provides lots of monsters in close area and elite packs which will keep the Nephalem Valor buff refreshed and maxxed.
This method can get you 10-12k gold every 2 minutes, and roughly 300k+ an hour.