hello i have 600$ coming to me for my birthday and maby a wee bit more
http://pcpartpicker.com/p/1bNBq
Well i changed out the motherboard for a better quality one. Chose cheaper ram and a 7870ghz. The 7870 Will beat the 660 by quite a bit. I have tested both and the 7870 beats it by 10-20 fps in some games. But all this came at a cost. The case you chose had to go if you wanted a better build. You can upgrade to a better case later on if you want. lastly i chose an xfx psu instead of a corsair builder. Just better quality parts thats all.
http://pcpartpicker.com/p/1bNF4