UPDATE 7800GTX IN 3 WEEKS
NVidia plans to unveil their next-gen graphics chip at an event in San Francisco on June 21. The event will be an "evening of full-throttle entertainment" with "revolutionary technologies, hot 3D content, and exciting gaming action as we unveil our next-generation GPU."
This desktop GPU will be very similar to the one they've designed for the PS3, dubbed the RSX or Reality Synthesizer, which has been said to be more powerful than two combined GeForce 6800 Ultras. The RSX has a 550MHz core clock and 300 million transistors.