a good card
I'd recommend an ATI Radeon 8500, retail version. They're about $150 from an online vendor such as Newegg.com. 8500's are loaded with features, come with a nice package of games, and give top-notch performance.
Another nice version of the 8500 is the Gigabyte Maya 8500LE. It's a few dollars less than the retail ATI card, but comes with big heatsinks and hardware-monitoring. It's clocked a little slower and won't OC quite as high as the retail cards can though. But the difference is marginal.
On the nvidia side... A geforce 3 Ti 200 is a good value... a little less $ than an 8500, and a little less performace too. Gainward, Leadtek, Visiontek, and Abit make some of the highest quality Geforce cards.
The Geforce 4 Ti's stand at the top of gamer graphics, and carry the price tag to prove it. But a lower-end Geforce 4 Ti such as a 4200 might be a good buy for around $180.
In the $100 range- geforce 2 Ti's, Radeon 7500's, and Geforce 4 440/460 MX's all rank about the same in speed. The 7500 has superior TV-out, as well as a DVI connection, and superb image quality.
Hope some of this helps you make a decision. Whta's your price range, btw?