There are two main manufacturers of the brains of a video card, the graphics processing unit, or Gpu, and each has its' advantages and disadvantages in each card it offers.
Nvidia and Amd/Ati both offer everything from entry level to world class gpu's and video cards.
Nvidia video cards have many features that make them great.
3D vision surround technology which allows you to spread your display across 3 or more monitors in full Hd 3d for an immersive experience and Gpu direct which allows for faster communication between computer hardware are two features that set Nvidia cards apart.
Optimus technology which optimizes notebook pc's, and purevideo high definition video processor are a few of the other features that help you get the most out of your computing experience.
Some Nvidia cards also feature Cuda architecture which allows the Gpu to perform mathematical calculations to speed up computing performance.
PhysX gives the card the ability to run real-time physics in games and Sli technology allows you to link together multiple video cards for increased graphics power.
With a great lineup of features it's no wonder that Nvidia is a popular choice for games and Amd is great for 3d rendering features.