Right now at newegg you can get this for $255: ATI OEM SAPPHIRE RADEON 9800 PRO 128MB DVI/TV 8X AGP
or this for $227: ATI All-In-Wonder RADEON 9700 PRO 128MB DDR 8X AGP
Both are refurbished cards, but those are great deals imo.
I'd get the AIW 9700 Pro because it's an AIW and it's not that much slower than a 9800 Pro.
If you're not willing to pay that much for a card, there's also the 9600 Pro for $156 : Sapphire Atlantis ATI RADEON 9600 PRO 128MB 8X AGP DVI/TV RETAIL.
In any case, please don't get an nvidia card. They're slower, the image is equal or worse than ati, especially with AA and AF, and like BigB said, they have problems in DX9 titles, like HL2.
The FX5950 just came out and it got owned by the 9800XT. It's the exact same price AND the XT comes with HL2 free (a coupon actually).