I'd have to say this is completely unexpected, but even my crap GFX 5600
plays Doom 3 like a bat outta' hell on High Quality settings! Well
maybe not a bat out of hell, but certainly very smooth and much better
than I ever expected.

Up until now, and from experience with the alpha, I had thought a low
end GFX card would be up the creek in Doom 3, but apparently not. The
engine is much faster and more highly optimized than I could ever dreamed.

I'd have to say anything from a GFX 5500 on up, or maybe a good
overclocked 5200 Ultra will do extremely well. 5700's are sitting very
nicely currently. The FX's aren't so bad after all.