Microsoft is offering a free e-Book version of "Introducing Windows Server 2008 R2" in your choice of PDF or XPS formats. There's no real catch, though you must have a Windows Live ID to get the download.

Free e-book offer from Microsoft Press – Introducing Windows Server 2008 R2
Learn about the features of Windows Server 2008 R2 in the areas of virtualization, management, the web application platform, scalability and reliability, and interoperability with Windows 7. Sign in to download Introducing Windows Server 2008 R2, written by industry experts Charlie Russel and Craig Zacker along with the Windows Server team at Microsoft.

Thanks very much to William Proffit for the tip!