The Evil Hat crew have created one of the few real e-books in gaming. For $5,
you can buy Spirit of the Century for the Kindle now!
It's a typical .mobi file: you have all the usual control over font and color, the artwork is embedded, and so on. It's hyperlinked out the wazoo with a very detailed table of contents. (It's also got a very nice feature with stunts: the name of the skill it's associated with appears in its heading, so if you jump right to a stunt description, you get the context painlessly. This is the kind of touch that marks great design.)
This is, to my taste, an actual e-book in a way that the vast majority of PDFs aren't. It's a pleasure to read. I highly recommend it!