The GeForce FX 5200 by nVidia is still amoungst us, but no high-end card from them in a Mac.... (not now, anyways).
The GeForce 4 Ti 4600 is still a BTO card in the G4. The Geforce 4 is built by Apple, BTW... included the ADC. That's why this card is so terribly expensive.
You're right about the 9000. But as this card is an OEM card aswell, I expect Apple + ATi made a joint effort to keep this card as low cost as possible. The 9000 is not a high-end card by any means, thus should be very cheap.
ATi is now the only high-end grfx card manufacturer for Mac. If you want the highest framerates, you must have the Radeon 9800, either retail (no ADC), or G5 BTO (with ADC). I do expect nVidia to come back with a shout, though.. especially after the ATi/nVidia -xBox trouble.