Well, you can't really go wrong with the Quadro's (NVidia) or FirePro's (ATI).
Going with gaming cards, such as Geforce, or Radeon's, can be a bit risky, as they seem to be hit-and-miss depending on your computer's setup. A setup for one person, may not work for another. If you are going to go for a gaming card as they are much cheaper, go for the Radeon's, as they have been OpenGL support. Any geforce's that we have at work have major issues with Maya.
You also want to make sure you get a card with a good amount of ram on it. (512mb+) This will dramatically increase how many textures and other graphic elements can be cached at one time.
Also look into upgrading your ram on your motherboard as well. This will also speed up your machine greatly.
If you need to, take a look at the official qualification charts for Maya. http://usa.autodesk.com/adsk/servlet...&siteID=123112
Imagination is more important than knowledge.