The EVGA GeForce GTX 285 graphics card is now being listed on the online Apple Store in the US and Canada. The GTX 285 is listed as being compatible with the "Early 2008" and "Early 2009" Mac Pro models and is priced at $449.95.
Currently the card is listed as shipping in 1-2 weeks and is not currently available as a build-top-order option on new Mac Pro models.