Effective today (Monday July 1, 2013) Windows Small Business Server 2011 Standard has reached ‘End of Sale’ status for the retail version.
Source: http://go.microsoft.com/fwlink/?Linkid=257790
You have until Tuesday December 31, 2013 to purchase SBS 2011 Standard OEM version.
Update 7/1/2013: Handy Andy says that you cannot purchase SA for SBS 2011 anymore.
Tip: If you’re buying the OEM version remember that
you have a 90-day window after purchase where you can add Software Assurance to the OEM version. If you don’t add SA, the OEM version is legally locked to that hardware forever.
http://blogs.msdn.com/b/mssmallbiz/archive/2006/05/22/604221.aspx