I copied the proposal from my user page over here for further discussion. Please add to (or subtract from) it as you see fit. This is a group effort, and I am excited to see what improvements the community has to offer to the proposal and the logo itself. ~ Ezra Katz 00:22, 22 April 2008 (UTC)
The main feature is a book seen from the side, with its pages fanning out in a semi-circle. The pages are moving, giving the feel of the dynamic nature of the wiki medium. The book is open too, alluding to the free nature of the Wikibooks project.
The text uses two fonts. The "WIKI" part is Gill Sans Regular. The "BOOKS" and other text is Garamond Bold. The sans-serif font embodies the spirit of a wiki: cutting edge, fast and modern, whereas, the serif font is classic, thoughtful, and warm. The pairing of these fonts represents the goals of this project to adapt the centuries' old art of book publishing to 21st Century technology and collaboration.
The logo is immediately recognizable as a book, while maintaining a unique image. The level of detail is moderate, allowing it to still be legible at all but the smallest scales (for which an alternate version is provided). The monotone versions are ideally suited for printed texts and would make a distinct impression embossed on the spine of a book.
Branding and Internationalization 
For the sake of creating a strong "Wikibooks" brand, the "WIKIBOOKS" portion of the logo should remain unchanged in different language projects. Localized versions can change the optional, bottom line of text to reflect the difference in language.
It is very common for an international organization to use an english name exclusively in its marketing. Unifying the multilingual projects under one name can only improve the recognition of the "Wikibooks" brand. Anywhere in the world, if someone types wikibooks.org into a browser, she can find the project in her own language (if it exists).
In a larger sense, a book created by this project is no mere textbook; it is a wikibook. Like Kleenex® is synonymous with facial tissue, or Band-Aid® is synonymous with an adhesive bandage, a wikibook should be what the whole world thinks of when they think of an open-content, collaboratively written text.
Official Colors 
The official colors for the logo will be the browns and grays of the logo below. This is a neutral color selection that gives a sense of authority and trust for our readers, and helps to establish Wikibooks as a reliable resource. Grayscale and monotone versions are also provided.
Unofficial Colors 
The official color scheme works for Wikibooks as a whole, but it does not reflect the diversity and unique nature of our community. Individuals can express themselves by picking their own colors to compliment the wikibook on which they work. For example: a wikibook about the environment can use a green version of a logo, or a wikibook on Anarchy could use a red version. The Wikijunior logo at the bottom of the page is an example of how one can change the color of the logo to appeal to a different audience, while retaining a connection to the overall Wikibooks brand.
Different Sizes 
With the rest of Wikimedia 
|Meta-Wiki - Coordination||Wikipedia - Encyclopedia||Wiktionary - Dictionary|
|Wikibooks - Textbooks||Wikisource - Sources||Wikiquote - Quotations|
|Wikispecies - Species||Wikinews - News||Wikiversity - Learning tools|