A Radeon 9800 Pro:
http://www.overclockers.co.uk/acatal...00_Series.html
They are faster than even the NVidia FX5950 in most games and are ridiculously cheap at the moment.
If you want the ultimate card, then get one of these:
http://www.overclockers.co.uk/acatalog/X800_Series.html
I'm waiting for the Sapphire X800XT to become available at the bottom of the page myself...

Forget NVidia, they cost about £100 more for less performance.