Today is the day: SQL Server 2016 is available for download!  You can download all the versions (enterprise, standard, web, express with advanced services, express, developer) of SQL Server 2016 now if you have a MSDN subscription, and you can also create an Azure VM right now that includes SQL Server pre-installed with one of the versions (enterprise, standard, web, express).  Lastly, you can also experience the full features through the free evaluation edition (180 days) or the developer edition (you have to sign in to Visual Studio Dev Essentials, a free developer program, before you can download the developer edition).

Here is a quick overview of the tons of new features, broken out by edition (click for larger view):

and here is another view on the features available for each edition (click for larger view):

More info:

SQL Server 2016 is generally available today

SQL Server 2016 e-book