@Kay
Complete AmigaOne Systems listed by Eyetech has listed an ATI Rage in the low end system and an ATI Radeon 8500 for the high end.
AFAIK, none of the newer 9000/9500/9700 cards are guaranteed to work, although hopefully we'll know for sure nearer the time of release for OS4. This would apply to the OEM cards licenced by ATI as well.
-john