Microsoft has officially announced the 4 editions of the upcoming Windows Server 2012.The versions are namely Data Center,Standard,Essentials and Foundation.With the Small Business Server getting dumped this time around.

This is the first time around that Microsoft has simplified the editions for as small as 4 number of editions for the Windows Server 2012.We also saw a similar change in the SKU’s for Windows 8 desktop operating system with smaller number of SKUs.
The Data Center edition which is targeted towards the bigger data centers with highly virtualized private & hybrid cloud environment,with full Windows Server functionality.The Standard model is suitable for non virtualized environments.While the Essentials edition is made ideally for the Small business environment.While the 4th edition which is Foundation edition has been designed for economical server usage and is only available to OEM’s.
Though the general availability is yet unknown at this time,but it is expected some where in the time frame similar to Windows 8 public release.
Source[Microsoft]