I have came through below wiki article on Microsoft technet, which have a nice collection of eBooks and articles on Microsoft Technologies.

Download content for SharePoint, Lync, MS Office, SQL Server, System Center, Visual Studio, Web Development (asp.net), Windows Server, Window Azure, Windows Phone and other Microsoft technologies in e-book formats (references, guide, and step-by-step).

E-Book Gallery for Microsoft Technologies

Source: social.technet.microsoft.com/wiki/contents/articles/11608.e-book-gallery-for-microsoft-technologies.aspx (Monica Rush)
Source: mstechtalk.com/collection-of-e-book-and-articles-on-microsoft-technologies/ (Adnan Amin)