What are some of the best video cards I can get for my computer?

I have Windows 7,a coolermaster PC box, dual quad core 3.0 MHz each Athlon, 8 GB of RAM and 2 TBs of hard drive currently I have a nvida physx286 video card I'm very disappointed in its quality. It takes forever to render animation and I love playing command and conquerors and the game crashes right when I'm about to kick butt. I want a video card that will kick butt. Anybody have some suggestions on what kind of video card and how much are they about? I appreciate your input|||Personally I like the Nvidia GeForce GTX 560 Ti



Nvidia GeForce GTX 570

AMD Radeon HD 6970

AMD Radeon HD 6950

Nvidia GeForce GTX 560 Ti