Eric Ligman has shared 2 great posts about a lot of free ebooks to download

Here are some books’ titles:

• Moving to Microsoft Visual Studio 2010
• Programming Windows 8 Apps
• Programming Windows Phone 7
• Office 365 – Connect and Collaborate virtually anywhere, anytime
• Introducing Microsoft SQL Server 2012
• Introducing Windows Server 2012
• Understanding Microsoft Virtualization R2 Solutions
• etc….

Here are the 2 posts , it contains more than 60 free books (first post, second post)

Also there is an E-Book Gallery for Microsoft Technologies where you can find more