Microsoft Press have released a free ebook called Introducing Windows Server 2012, which does exactly what it says on the tin.

There are three versions available, depending on where you want to read it:

Introducing Windows Server 2012 RTM Edition – PDF ebook
Introducing Windows Server 2012 RTM Edition – ePub format
Introducing Windows Server 2012 RTM Edition – MOBI format

I read the version of this book that was based on the beta and found it very informative. It’s now been updated to the RTM version, so there’s no reason not to grab it now.