Microsoft SQL Server 2005 Express Edition Service Pack 3

From Microsoft: Microsoft SQL Server 2005 Express Edition (SQL Server Express) is a free, easy-to-use, lightweight version of SQL Server 2005. It is fast and easy to learn, allowing you to quickly develop and deploy dynamic data-driven applications. SQL Server Express provides powerful and reliable data management tools along with rich features, data protection, and fast performance. It is ideal for embedded application clients, light Web applications, and local data stores. Designed for easy deployment and rapid prototyping, SQL Server Express is available at no cost, and you are free to redistribute it with applications. If you need more advanced database features, you can upgrade SQL Server Express seamlessly to more sophisticated editions of SQL Server.