Best is a bit of an open term. This is the "best" video card for Vista http://www.newegg.com/Product/Product.aspx?Item=N82E16814161399,
do you want to spend over $500 on a card?
Need to start with your budget, your computer brand and model, power supply wattage, what you want the video card for (high-end games, light games, HD video, etc....). For light games, video, about a $40 card will do.