Otis,
The ATI 9650 256MB card that comes standard with the new dual 2.7Ghz G5 has one single link DVI and one dual link DVI so you can hook up a 23″ and a 30″ Cinema Display with this card. But if you need more juices, then the NVIDIA 6800Ultra is the way to go but it eats up the next PCI slot because of the fan. If you need a 512MB card that can support the 23″ and 30″ Cinema Display and does not eat up a PCI slot, then go with the ATI X800XT card. Also, if you intend to get the FinalTouch color correction software as Wally mentioned, you will need to stick with ATI cards, so the X800XT is probably your best option. To lose a PCI slot on the G5 can be an issue for some people.
Also, AJA has a HD to DVI converter called the HDP (https://www.aja.com/hdp.htm) which features hardware scaling to take care of the 4:3 and 16:9 aspect ratio. If you need to connect to 4 DVI displays, they have a new one called HDP4 (https://www.aja.com/hdp4.htm).
But all in all, Kona 2 is a fantastic product.
-chrispy