EVGA Serves Apple Users a GeForce GTX 680 Mac Edition Graphics Card
EVGA's card shares the same specifications as NVIDIA's reference design, meaning the base and boost clocks check in at 1006MHz and 1058MHz, respectively. It also has 2GB of GDDR5 memory clocked at 6008MHz (effective) on a 256-bit bus, 1536 CUDA cores, and several key technologies, such as NVIDIA GPU Boost and support for up to four concurrent displays.

EVGA says the Mac Edition part will work on Mac Pro models from early 2008 on up with Mac OX X 10.8.3 or later. It also fully supports Windows OSes in Apple Boot Camp, including Windows 8.
No word yet on price or availability.