I'd say the top echelon chips sets from the earlier generation, i.e. ATI R9800 and GeForce FX59x0 are 'enough' to get almost uncompromised image quality at comfortable playing framerates, in 'Far Cry'.
The gaming/value sweetheart of that generation is R9800pro 256-bit & 128MB. At around or below $200.
nVidia's corresponding goodie is probably the 128MB FX5900XT. Better at OpenGL interfaces than ATI, but probably not quite as fast at DX gaming. The R9800 also *cheats* in a very clever way (insignificant impact on quality, and all the new cards do the same.) on anisotropic filtering, which makes it loose less performance with AF.
Currently, there seem to be some competition from value echelon, of new generation chipsets, at the same price. I'm not fully aware of these, X600, FX6600, FX6800LE etc, and their capabilities and limitations. Sorry. They are probably interesting for you.
I personally intend to do some checking on the performance of the 6800LE, not for my own sake (I'm destined to 6800GTs), but on the behalf of some others. I haven't yet, sorry.
I have played through FC on a 128MB card, with mostly 'very high' settings. But actually, particularly this and perhaps future games, can actually have real use for 256MB. But you'll get along for a while on 128MB. Being conservative with AA and resolution, helps saving video memory, so you can use the richest textures and highest polygon counts, without performance penalties. And any game prior to FC, is no problem at all for 128MB, below 1600X1200.
My past experience is that ATI are useless (bugs) on tool-applications with OpenGL interface, while all GeForce, even the cheapest, are virtually flawless. For that reason, I prefer buying nVidia, since my cards eventually find their way into all kinds of utility PCs where such software is used. Since I haven't tested R9800 OpenGL in ernest, I cannot say if the problems persist with ATI.
But the ATI R9800 was the true gaming gem of its generation. And the 256bit R9800pro 128MB was the best value videocard. The pitfalls are the *false* R9800 cards, "9800SE" and some 128-bit "R9800pro". These are crap. Similar priced 'cheaper' chipsets like 9600xt, FX5700 etc, are actually better.
Edit: Once the GF4 Ti4200 was THE card to get. Then it was R9800pro. My money is on the 6800GT to become the next classic.