I just put together a guide on HubPages for a bidding strategy that will allow you to make some decent money playing Diablo 3. As stated in my short guide - understanding the gold auction house is the first step to understanding how to make money playing Diablo 3. Gold has a value and an exchange rate (if you understand how to convert the gold that you've acquired to real money. This guide will help you in one aspect of the gold auction house - bidding on items.
Check it out and enjoy!