Well, what games do you want to be able to play? There's a pretty large spectrum between entry-level and high-end, and you can spend as little as $30, or as much as $600 for a card. These days, you should at least have an nVidia GeForce FX 5200 or higher, or an ATI Radeon 9500 or higher. Some of the top models are the Radeon X1950 XTX, and the GeForce 7950 GX2. Don't bother getting anything that doesn't have the GeForce or Radeon label, those are either chipsets that aren't tailored to gaming, or chipsets by other companies, which don't have as good of performance or compatibility. Also, remember that, unlike ATI, nVidia only makes the chipsets. Third-party brands make the boards for them - companies such as XFX, BFG, PNY, eVGA, etc.