Barnes and Nobel came out with their NOOKcolor today which is really just a 7" Android tablet specialized for reading ebooks, specifically those from BN's NOOKbooks store. This got me thinking that the killer "device" that everyone is trying to create should really be a original NOOK (e-ink) on one side and a NOOKcolor on the other side. Take the devices and glue them back to back. Call it a NOOKflip. You can browse for books and use all your apps on the color side, but when's time for serious reading, the e-ink side is there. Of course, these two screens would share the same OS, hardware, and storage.
Really though, Apple should adopt this idea in their iPad (and possibly their iPhone and iPod Touch) and add an e-ink screen to the back. These new devices would be a full iOS device but with an e-ink option for reading books, PDFs and long websites. But you can still run all your apps, games and watch movies on the beautiful, color LCD.
The best solution would be a screen that can do both e-ink and color LCD. While I'm confident some people are working on this, I'm afraid it's a couple years off.