Well this is pretty interesting. Over at Sony Insider, a user at the forums has just posted the service manuals for the PRS-300 and PRS-600 Sony Readers, which haven't even been released yet.
Since the PRS-700 is no longer on sale, these new Readers may very well be on the way shortly. I mean, these manuals were just printed this month. A few details include the PRS-300 will have three color options (silver, black and red), a 5-inch screen and 440MB of storage.
The PRS-600, on the other hand, will also have the same color options but a 6-inch screen, 440MB storage and MS and SD card support. Full feature sets are not yet known, so we'll be sure to let you know once that info is released.