I will build an ubuntu system and I want to have as many visual effects as possible, which graphics card should I prefer and why?
I do not intend to play games, I'll just work very long hours there and the eye candy helps a lot.
Honestly, any graphics card from the past two years or so will be more than enough for desktop eye candy. My notebook doesn't have trouble with them, and it's been two years or so since that was anywhere close to being 'new'.
In my experiences the best cards are either Intel or Nvidia. Unfortunately the Intel cards usually have poor Direct Rendering support so I've found myself going for Nvidia with the proprietary drivers more often than not. A GeForce 7600 GT is a great card for a Linux box.
Nvidia's driver support is what attracts me the most. ATI and Intel have very little support for the Linux community.
I prefer Intel GMA graphics cards. The driver is open so they get good community support. You don't have to worry about any 'freedom' related issues with closed drivers. Right now my Dell Ubuntu laptop with an Intel GMA is running the "Extra" visual effects.