Out of interest, (is the mainboard the card is going into) AGP or PCI-E?
Regardless, right now the GeForce 6800 GT/Ultra is pretty much your best 'bang for buck' I'd say. With GeForce 7 released, not to mention ATI's new competition due out later this year, prices are likely to drop to the very affordable bracket. My XFX* 6800 GT (AGP) served me hulluva well, overclocked like a beast too.
*The manufactuer of your nVidia card is important. A lot of people have bad things to say about XFX, but from personell experience I see them as great; I never had any issues attall with my GeForce 6. Otherwise, eVGA, BFG, Gigabyte, Leadtek are all trustworthy brands.
AMD X2 4400+ Toledo 1MB/Asus A8N-SLI Deluxe/2GB Kingston HyperX/SLI Gigabyte 7800 GTX 256MB/Creative SB Audigy 2 ZS Plat w/ Creative Inspire 6.1 speakers /180GB Hitachi PATA/19\" AG Neovo F-419 LCD/OCZ PowerStream 600W PSU/WinXP Home SP2