Nvidia and AMD flavor, each have strengths in certain games (especially mantle for AMD) so look those up first.
$480 After Rebate EVGA GeForce GTX 780 3GB Dual FTW ACX
http://www.newegg.com/Product/Product.aspx?Item=N82E16814130951&nm_mc=AFC-C8Junction&cm_mmc=AFC-C8Junction-_-na-_-na-_-na&cm_sp=&AID=10446076&PID=3938566&SID=
$480 After Rebate Gigabyte Radeon R9 290X 4GB WINDFORCE
http://www.newegg.com/Product/Product.aspx?Item=N82E16814125499&nm_mc=AFC-C8Junction&cm_mmc=AFC-C8Junction-_-na-_-na-_-na&cm_sp=&AID=10446076&PID=3938566&SID=