I would just like to highlight the SQL Server 2005 Compact Edition.  The download page is here  This is the latest SQL Server Compact Edition add-ins, updates, tools and all the parts to enable you to build occasionally–connected mobile and desktop applications.  To find out more about the product go to the SQL Server 2005 Compact Edition Page.   There are product overviews, news and access to resources.  Links for some of the downloads are below.  The new Blog is for the product is sql server compact edition.

 

Download the SQL Server 2005 Compact Edition Runtime Engine

This link prompts you to register before download.  You get lots of free stuff and you need to if you want to re-distribute with your applications.

 

Install the SQL Server 2005 Compact Edition Developer Software Development Kit (SDK)

The software development kit has all the files required for installing onto mobile devices.

 

Read the End-User License Agreement for SQL Server 2005 Compact Edition Device SDK

 

Additional

SQL Server 2005 Compact Edition Books Online

 

SQL Server 2005 Compact Edition Tools for Visual Studio 2005 Service Pack 1

 

SQL Server 2005 Compact Edition Access Database Synchronizer

 

SQL Server 2005 Compact Edition Server Tools