ASUS's GeForce GTX 680 which would feature the latest 28nm GK104 Kepler Core has been listed for Pre-Order by US retailer Bottom Line Telecommunications for a price of $566.75. Zotac's GeForce GTX 680 was also put on listing on a few online retail sites which you can see here.
The product model " GEFORCE GTX680 PCIE 3.0 2GB GDDR5 28NM GUP 3D VISION SURROUND " would be a reference edition featuring stock clocks of 1006MHz Core and 1504MHz (6GHz Effective Memory). It would feature 1536 Cuda Cores, 2GB GDDR5 Memory, 195W TDP and performance around 10-20% better than the HD7970 as seen from the benchmarks here.
You can find the listing here.