As much as I love books, the kind that can be held in one's hands and flipped through at will, the idea of online books is also something I appreciate for a number of reasons, such as saving on paper use, availability to a wider audience, and the potential of formats different than double-sided pages bound together. Here's a couple online books, as different from each other in subject as in execution.
Piel.Skin by Ethel Baraona Pohl
Pohl presents a Flash-based book with 25 contemporary projects around the world. The Flash format allows for an interactive world map for the projects, with Google Maps links for each accompanying some text and images. A very well done "book" that shares some characteristics (and projects) with my weekly page.
Architecture and Memory by Robert Kirkbride
The New School's Kirkbride expands upon an essay included in volume four of Chora (I reviewed it on my weekly page), a study of the late 15th-century Renaissance Studios of Federico da Montefeltro in Urbino and Gubbio, Italy. The online book is a generously illustrated version of a text-only book to be published in December by Columbia University Press. Kirkbride looks at "architecture's capacity, as a discipline and medium, to transact between the mental and physical realms of human experience."