So... keep in mind that whatever your GPU now, you won't get the same performance as you will on an Intel build. So any benchmarks will be relative, because they'll have been tested on Intel builds. I'm assuming your budget is $500 for the REST of the build... so here're some of my suggestions:
RAM: 8GB DDR3-1600 CAS9 1.5v RAM... G.Skill Vengeance is nice... it's on newegg - $45
GPU: MSI Twin Frozr II OC 7850 - $260
HDD: 1TB 7200rpm. There's one on newegg with good reviews and it's $99.99 plus $1 shipping...
I have no idea about AMD CPU coolers. I know that the Hyper 212 Evo is a favorite for Intel, and it says it's universal and will fit on AMD boards... but I don't know for sure.