Total budget? Remember not to skimp on the PSU. High wattage is not important, but high quality is. A 380W Antec Earthwatts can run any graphics card needing only a single PCIe power cable; a "600W" Diablotek would probably choke, smoke, and croak on a HD7850.
A GTX650Ti Boost Edition or HD7850 should be able to play any game at 1920x1080 on "good" settings. Pair it with an i3-3220 or FX-4300 for a decent budget gamer. The latter will likely need to be overclocked. I use and recommend the Xigmatek Gaia over the inferior but more commonly mentioned Hyper212 EVO:
http://www.techreaction.net/2011/07/07/review-xigmatek-gaia-sd1283/7/
http://www.techreaction.net/2011/11/27/review-cooler-master-hyper-212-plus/4/
Unlike the Hyper212 EVO (ignore the URL; it IS the EVO they tested), the Gaia never throttled, although it wasn't always the coolest depending on the fan used. Both got awards, but if you factor in the price, the Gaia wins hands down.