This free eBook is available on BlenderWiki, the wiki site that acts as the online documentation for Blender. Written by John Blain and aimed at beginners, the book is 305 pages long and covers all the major topics on Blender from version 2.54 and up.
At first site the book looks good and it is accompanied by several color images. As those who purchased any of the printed books on Blender know, this detail alone arguably makes the book better than several of the printed books out there.
The book is focused on the Windows version of Blender. It is a downloadable file in PDF format. Click the above link to go to the download page.