Anyone One Help Me Buy GPU

My Computer Specifications

Mainboard-Esonic G41 CDL PCI Express x16 slot And Gigabyte -G41 Combo
Intel® Core™2 Duo Processor E4500 (2M Cache, 2.20 GHz, 800 MHz FSB)
Ram-2GB And I am buy Graphics Card then upgrade 4GB
I Like Play Game But My System Configuration who is best GPU And i am buy
anyone help me plzz...