I think you may need to post a few more details about your system specs and intended use for your PC before anyone will really be able to provide any constructive comments. Post a few more details and see if that improves the responce to your question. ;-)
I guess I should also have added the question how much do you have or are you willing to spend? The problem with graphics cards is that you can spend anywhere between £30 and £400. I recently changed the GFX card on my other machine from a Radeon 9500 Pro (due to a fault with it) to a X800 Pro. The former cost about £150 and the later twice as much. TBH I had no plans to change the card so soon and only done so because of the fault (artifacts due to heat).
Needless to say the X800 Pro does perform better and allows me to play games with video settings cranked up, although TBH I feel a 9800Pro or equivalent would still do a very good job. Certainly I used to have no great difficulty with Half-Life 2 when using the 9500Pro.
Hope this is of some help, perhaps someone else wil jump in with some more suggestions in a moment. :)
have geforce fx5900 (not the cut down version GT or something like that) on my pc running 2500+. plays farcry at fairly good rate (medium settings). dont know about doom3 of H/L 2 as use xbox for games mainly.
Thanks man but, if anyone else knows, i was wondering what is the limit of my cpu? like if i get a 6800 then my cpu won't be able to get the full performance out of it. does anyone know up to which card my cpu can handle?