The Phenom X6 CPUs' extra cores are not helpful in gaming.
On this budget (w/o monitor, peripherals) you could go Intel for a higher-performing machine, like so:
$220 i5-2500K
$115 Gigabyte GA-P67A-D3-B3
$020ish DVD
$060ish 1tb HDD
$060 Antec 300
$110 Corsair TX750 (for Xfire) $95 after rebate
$050 8gb RAM (probably 1333)
$030 Hyper 212+
$100 Windows 7 Home
$765, leaving $215 for the graphics card, or $315 without the OS.
^+1 megaman, do you need peripherals or the OS? If you need neither, this is a feasible build, because you'll be able to get a nice GPU. If you do need Windows, maybe you should stick with AMD.
$220 can get you a 560 Ti (I was surprised to find it) at
http://www.newegg.com/Product/Product.aspx?Item=N82E16814261100
But if you're getting a Ti, you could go AMD and just save money. So it all comes down to Windows, or else to whether you're willing to spend more on a GPU.