You'll need about a hundred, following choices are, nvdia 9800 series, nvidia 250 series, or a ATI 4850. I did not put these in a specific order, just suggestions.
You can goto to Tomshardware, google it, and there will be reviews and articles for you to read. Also at Tomshardware review there is charts and you can compare cards.
I prefer EVGA or XFX, this is for the lifetime warranty. I think BGP is lifetime. Just my personal preferences.