$685, no OS though. http://pcpartpicker.com/p/eN7s
Should handle current games fine, and if you overclock that Phenom you should hit almost 4GHz. So for $685 you get a Crossfire capable motherboard incase you want to buy a second 7850. A decent quad core CPU, 8GB of RAM, 2TB of storage and a good video card. You will be able to play just about any game on high to max settings pretty easily.