Pixel Shader 3.0 has been implemented for several years now.
Any nVidia card from the 6600's on up, and ATI 1300 forward will support Pixel Shader 3.0
As pointed out already, you just have to make sure the card you decide to get matches the type of graphic slot you have on your motherboard, that is the only correlation to worry about. (i.e PCI, AGP, PCIe)