DBAs and Database Developers always need to test new database-related work before migrating it to Production Environments.
To this end, Test/Development Environments are usually set up in order to allow for testing new administration and programmability features of DBMSs (in our case SQL Server :)
Though, by only having such an environment set up is not enough. DBAs as well as Database Developers need sample data in order to manipulate it with various SQL Server operations and record the "responses" of the underlying SQL Server objects (i.e. databases, logins, etc.).
For every version of SQL Server, Microsoft releases sample databases (and many other samples such as code examples, etc.) which allow the user setting up Testing Environments of SQL Server along with sample data, thus being able to easily test new functionality.
It is not random that many SQL Server examples found on blogs, forums and websites, are referring well-known sample databases such as: AventureWorks, Northwind, pubs, etc (well, my posts on Entity Framework use the "pubs" database :)
So, by using the links provided below, you can find SQL Server sample databases (as well as other sample stuff) for all the SQL Server versions:
SQL Server 2000
You can download the Northwind and pubs databases from the following link.
SQL Server 2005 and 2008
You can find community projects and samples for SQL Server 2005 or later on Microsoft CodePlex, on the following link: http://www.codeplex.com/SqlServerSamples
The sample databases link is the following: http://www.codeplex.com/MSFTDBProdSamples/
Well, that's it, I guess that now you can continue experimenting with the new features of the latest SQL Server release with using the latest sample data as well! :)