There's only really two graphics cards worth considering at the moment, now Nvidia have bought 3DFX.
The ATI Radeon 64mb,
or as pointed out any card that has the Geforce2 chipset. There's three cards that have this, the GTS, PRO and ULTRA. Each one has the same chipset but are clocked at higher speeds with the ULTRA having obscene amounts of power! But it is very expensive, the ULTRA could set you back +£300.
A few companies are producing boards with this chip,
Creative Labs,
Elsa,
Guillemot,
And I'm sure there may be more.
You really need one of these cards as any other card, expect maybe the Voodoo 5500, will cause bottlenecks in your system and thats the last thing you want having forked out for 1ghz of processing power!
p.s The ATI Radeon is a superb card and you can get it for under £200 in the UK. Computer experts say that it is one card that won't be rendered obsolete in a few months the way maybe the Geforce cards might be. (Nvidia produce new chips every 6 months).
The Radeon has enough features to keep anyone happy for ages.