First off, what's your budget?
What's your current PSU?
Without knowing the answer to those questions I would only recommend a Radeon 7750 (draws power from the PCIE slot, no external connections) or a Radeon 7770 (requires a 6 pin power connector from the PSU, which your PSU will not have if it's stock).
I am having a hard time finding your motherboard. Please download CPU-Z and see what it says under Mainboard.