If you want to supplement your collection of technical e-books, or you need in-depth information about Microsoft technologies, you may be interested in a set of works from Microsoft Press which are being offered for download free of charge.  

There are 10 books on offer, and you can see the titles in the screen shot below.  Topics include Windows Phone 7, SQL Server, Office 365 and Windows Server, as well as Visual Studio.

All are available in PDF format from http://blogs.msdn.com/b/microsoft_press/archive/2012/05/04/free-ebooks-great-content-from-microsoft-press-that-won-t-cost-you-a-penny.aspx