Nvidia finally got a successful silicon G80 chip out and this sets the G80 to be released somewhere in September. It will have 32 pixel pipelines and 16 vertex and geometry shaders. The Inquirer (where I got this information; theinq.net) thinks that Nvidia can clock it up to 700mhz.
As far as ATI's R600 which uses the unified shader approach will be Novemberish. This also means that ATI will need to launch their R580+ (which will be called the X1950 XT and X1950 XTX) before G80's launch if they don't want to be crushed by Nvidia on the spot. All three (G80, R580+, and R600) will be using GDDR4 memory and the G80/R600 will be using DirectX 10.
So far it's too early to tell if either the R600 or G80 will be stronger then each other and the R600 does have a 6-8 week release date after the G80 so they may still have time to tune up the R600.