depends what money you have but the very very very good cards ( use ebay or online to get better price)
1)x800XL 512MB (its a beast of a card)--plus it is ati which i like (drools)
2) the gefore 7800GTx is very very fast but too much money really
There are more cards on the market try
http://www.sapphiretech.com/ or
http://www.nvidia.com/page/home
but for value for money x800 XT or x800 PE
the gefore 6800 gt or 6800 ultra are amazing I have the x800pro which I have overclocked loads but it only has 12 pipelines ( not that it makes a huge problem becasue the arctic cooler and 540/540 overclock I have running helps loads). But it is best not to over clock so I would buy the X800PE or 6800 ultra for good soild value for money.That will last for ages and not bankrupt you.