Sony has announced it's $400 ebook. Intended to compete with the Amazon Kindle, the device costs $100 more than the Kindle but works with several open ebook formats, giving users access to a wider range of books.
Both devices are likely to founder. Everyone is sick of lugging around multiple devices, and worse, all the special cables and chargers needed for them. I'm kicking myself for buying a small Nikon camera without checking on the data cable--the camera uses a proprietary cable instead of more common mini-USB cable, meaning I now have to lug around yet another cable.
Enough information is leaking out now that it appears very likely that Apple is going to release a tablet device either this fall or in early winter. When it is released, it will kill both the Kindle and the Sony ebooks. A Apple tablet will support email, Web browsing, and probably thousands of applications, as opposed to the ebooks that do only one thing. We just don't have enough room in our bags and briefcases to lug around a laptop and an ebook device, and for a lot of us, a capable tablet will replace both the relatively heavy laptop and will also serve as a very capable ebook reader.
Book publishers are playing along with Sony and Amazon right now because they have to, and it's a good way to gain some experience with the economics of ebooks. But a more popular device that supports many book formats, not just one or a few, will swamp the competition. It's only a matter of time.