People have been talking about electronic replacements for books for quite some time. But Amazon may be the first company to offer a viable realization of the idea: Amazon Kindle. It can't read PDF files and your right to read the e-books probably expire in a few years - and consumers give it 2.5 stars only - but a zeroth approximation for USD 400 is here. Click the picture to get to amazon.com.
Sorry, the "electronic paper" screen is black-and-white.