Here is a short video showing some tips and tricks to make some money on the auction house. Basically he shows us how to turn 100g in to 3000g in less than 2 minutes using a commodity strategy on the Diablo 3 Gold Auction House.
Everyone knows you should buy low and sell high, but you might not be aware of the ENORMOUS opportunity for profits by taking advantage of the instantaneously updating auction house, and people that don't know how to use it.