Microsoft UK released free ebook for developers on ‘Building Windows Phone Apps’. Over 100 pages long book is written by the exports of Windows Phone platform, who are in the team and developed the platform. The book gives you useful and technical information about the platform with some stories of the people and the apps they have developed. This is really a great reference to developers to do better job with Windows Phone.
You can download the ebook here: Building Windows Phone Apps: A Developer’s Guide. The Initial release covers few topics and remaining will be added and chapters will be updated. Download your copy to become a good Windows Phone Developer.