For the best performance a a gtx 770 (330-350$) and go with an evga, gigabyte, Asus, or MSI for the best brands. My personal favorite is evga.
However if you want to save some money but still play the latest games the gtx 760 will also suit you well at a price of about 250$. Again go with evga, gigabyte, Asus, or MSI. It is the graphics card I run and it works very well.
But these are in you price range, with your system you could run most any single GPU.
best performance in this price range is a 290 and best bang for the buck would be a 280x.