If your MoBo is capable, given what you might get for a used 250, ya might wanna consider using it as a PhysX card. As far as recommendations go, it's hard to give ya anything w/o a budget and playing resolution. To give ya an idea of what peeps are buying these days, here's a list of what's most popular by measuring what's hitting Steam Serves:
Market Share Per Steam Servers
Card Description ----------- June Market Share ----------- January Market Share --------- % Change
NVIDIA GeForce GTX 560 -------- 3.46% ----- 9.47% ----- 273.70%
NVIDIA GeForce GTX 570 -------- 2.77% ----- 4.02% ----- 145.13%
ATI Radeon HD 6950 ------------- 2.54% ----- 4.08% ----- 160.63%
NVIDIA GeForce GTX 580 -------- 2.47% ----- 3.69% ----- 149.39%
ATI Radeon HD 6970 ------------- 1.26% ----- 1.72% ----- 136.51%
NVIDIA GeForce GTX 550 -------- 0.59% ----- 2.96% ----- 501.69%
$205
http://www.newegg.com/Product/Product.aspx?Item=N82E16814125363