It's slightly over your budget, but as the others have said, you really can't go wrong with a GTX 970. My 2nd and 3rd options would be either a GTX 760 or 770. Keep in mind you need at least a 600w PSU for the 770 and a 450w for the 760; you will need 500w for the 970. All three PSU requirement specs are taken from Nvidia's web-site.