Microsoft has announced that SQL Server 2016 will be available for general purchase and download starting June 1st 2016.   The four different editions include:

• SQL Server Enterprise 2016
• SQL Server Standard 2016
• SQL Server Express 2016
• SQL Server Developer 2016

A datasheet comparing the features of each edition can be downloaded from here.

SQL Server Developer 2014 and 2016 will continue to be free per Microsoft.

SQL Server Express 2016 may be downloaded from https://www.microsoft.com/en-us/download/details.aspx?id=52679