The most striking electronic ``book'' I've ever seen was the Corbis _Leonardo da Vinci_ multimedia CD-ROM --- a presentation of the Codex Leicester which Bill Gates had purchased at auction and other materials:
http://www.businessweek.com/1996/49/b350428.htm
Things like the Periodic Table of Elements app for the iPad are blurring the distinction between book and app --- it'll be interesting to see other things like to that.
Similarly, the website for the book _Bembo's Zoo_ is much cooler (if you have Flash) than the printed version:
http://www.bemboszoo.com/Bembo.swf
William