Bright Side of News claims NVIDIA's GeForce GTX 560 should start sampling by the end of January:
Multiple sources informed us of GF114 reaching clocks as high as 930-940MHz for the GPU on air, meaning aggressive overclocking manufacturers such as EVGA or Point of View might even offer an overclocked GeForce GTX 560 with all 384 cores ticking at 1.8GHz. Just like majority of 40nm silicon made by TSMC, you should be able to reach 1GHz or come very close to it once you deploy more efficient cooling, such as waterblocks.
Our sources disclosed that the sampling date for the parts should start in the dying weeks of January, giving enough time for a product launch after the Lunar New Year celebrations. Naturally, all is subject to change, but our sources were adamant that GTX 560 will ship on time and has no problems in beating Barts [Radeon HD 6800 Series] by a significant margin.