I had the same CPU paired with a 9800GTX (was a beast in its day) and imo the best pairing with that CPU (and you can pick them up for next to nothing). If you want to push it to the limit a HD 7770 or GTX 650Ti will work without to much bottleneck.
As a note the minimum recommended PSU for the HD 7770 is 500w the 650ti is 450w