Just in case anyone is looking to pick up cheap graphics cards, the end of GPU mining is here.
If electricity is 15¢/kWh, there is no longer any profit to be made mining with a 40nm GPU (HD 5000/6000 series). For people like me where electricity is really cheap (7.7¢/kWh). I calculated that I should turn off my 6970 when difficulty reaches 30 million, which should happen within a month.
The 28nm HD 7000 series should last a little longer, but I calculated a difficulty of 40-60 million (15¢/kWh to 7.7¢/kWh) being unprofitable, which would be sometime around late July if the current trend of difficulty increase continues.
Look for a flood of GPUs on the market in the coming months causing used GPU prices to crash. Keep your eye on the market and you might be able to snag a good deal.