You can pretty much put any card that you can afford and that will fit. Have you looked inside the case at the motherboard and at the x16 slot which is the slot closest to the cpu socket. Alot of video cards are about 9 or 10 inches in length so you would have to see how much space there is. The next thing is the price and how much are you willing to spend? Next is what do you want to get the card for ? Is it for gaming or productivity or both?
EVGA 01G-P3-1561-KR GeForce GTX 560 Ti FPB (Fermi) 1GB 256-bit GDDR5 PCI Express 2.0 x16 HDCP Ready SLI Support Video Card
$229.99 and a $30 rebate makes it $199.99
http://www.newegg.com/Product/Product.aspx?Item=N82E16814130623
XFX HD-687X-CNFC Radeon HD 6870 2GB 256-bit GDDR5 PCI Express 2.1 x16 HDCP Ready CrossFireX Support Video Card
$219.99 and a $25 rebate makes it $194.99
http://www.newegg.com/Product/Product.aspx?Item=N82E16814150563
XFX Double D HD-685X-ZDFC Radeon HD 6850 1GB 256-bit DDR5 PCI Express 2.1 x16 HDCP Ready CrossFireX Support Video Card with Eyefinity
$154.99 and a $15 rebate makes it $139.99
http://www.newegg.com/Product/Product.aspx?Item=N82E16814150515
EVGA 02G-P3-1559-KR GeForce GTX 550 Ti (Fermi) 2GB 192-bit GDDR5 PCI Express 2.0 x16 HDCP Ready SLI Support Video Card
$159.99 and a $10 rebate makes it $149.99
http://www.newegg.com/Product/Product.aspx?Item=N82E16814130652
So here are a few cards to give you an idea as to what prices are and what you can get depending on what you are using it for.