Hardwareanalysis has posted a preview of ATI's upcoming X1800 series. Here's a short snip:
ATI is about to introduce their next generation graphics card based on the R520 architecture which will be launched as the Radeon X1800 series of cards. We put it up against the capable GeForce 6800 and 7800 series to see how it performs. Read more at Hardwareanalysis.
However, be aware that this preview might be biased as you can read at DriverHeaven.