For a while now, databases have been the defacto storage mechanism for almost all types of software -- be it Web, Desktop, and now Mobile -- whether connected, occasionally connected, or standalone.

Microsoft has a whole stack of solutions (SQL Server, SQL Server Express, SQL Server CE), but there are other solutions that can, depending on your requirements, be used.

There's no hard and fast rule to follow, but -- in general -- most .NET developers use either SQL Server or SQL Server Express for web development (although those coming from a PHP background also prefer MySQL), SQL Server Express for desktop development (although I'm starting to see use of SQL Server CE and/or SQLite for this role as well), and SQL Server CE and SQLite for mobile development.

Each platform has its own set of downloadable freeware/shareware tools and GUI's, which as I develop the pages, you can find links to below -- or simply use the site's navigation menu above or to the left.