Ubisoft is going to be releasing this Assassin's Creed Encyclopedia in November 2011.
At 256 pages, it's going to have a detailed look at the stories, characters, history and the other AC merchandise.
Here's the making-of video for the book:
You can check out more information and order the book at:
Unfortunately, this book isn't available on Amazon, and after reading the readers' comments there, it seems that shipping cost is going to be astronomical.
Maybe some reader here can get it and review it on the forums.