Server 2012 (Formally Windows 8 Server) Release Candidate Datacenter has been released:
Download Page: http://technet.microsoft.com/en-us/evalcenter/hh670538.aspx
I can tell that Windows 8 RC will be released very soon. 
Windows Server® is the leading server operating system that powers many of the worlds’ largest datacenters, enables small businesses around the world, and delivers value to organizations of all sizes in between. Building on this legacy, Windows Server "8" delivers hundreds of new features and enhancements for transforming virtualization and cloud computing to help you reduce IT costs and deliver more business value. Within Windows Server "8" you will find exciting innovations in areas of virtualization, networking, storage, user experience, and a transition to Windows PowerShell® to take scripting to a whole new level.