Good Video card for my custom computer?

The video card on my custom computer is going out and it wasn't that great in the first place. The computer has this motherboard:http://www.asus.com/Motherboards/AMD_AM2…

and this Power supply:http://www.geeks.com/details.asp?invtid=…

I casually game so I want a good video card but not something over $500 what would you suggest for this set up? It also has 8GB's of RAM and Windows 7 if that makes any difference

Also I'm not changing the power supply so just tell me what is the best i can get for what I have|||If you are what you say you are (casual gamer), then a GTX 550Ti would do more than well for you.



If you are actually a hardcore gamer, you should go for the GTX 570 - not to high price, great performance.