Personally I have using Geoforce cards for the last few years and have loved the quality of the cards and the drivers (I always use the Nvidia reference drivers). As with anything computer related you should buy as far up the curve as you can, since it will delay the inevitable upgrade

If I remember correctly the current top of the line for the Nvidia cards is the Geoforce 4 Ti series. But I think I read that they are about to release a new chip set soon.