Today, O'Reilly released my book, The Geek Atlas, as an iPhone application. It's the complete text of the book on the iPhone. Since the book is organized as small chapters it's very readable on a small screen.
The neatest feature is that latitude and longitude given for each place in the book is clickable and takes you straight to that location on Google Maps.
And it's only $5.99 or £3.49.