Desktops eh? Well in that case, you should look at NVIDIA 6600+ series. Again with the 128 or better yet get the 256MB Memory size. I don't think you need to concern yourself with the 512 or even the 1GB sizes.

Key features to look for are: 128MB or 256MB memory size, GDDR3, PCI or PCI-e, =>12 Pixel Pipelines, and make sure your motherboard can support it. I'm more familiar with NVIDIA cards than I am with ATI cards. I like both its just I have had good experience with NIVIDIA. Brand names shouldn't really matter, just as long it has those key features for your computer.