SQL Server 2005 Enterprise Edition
Enterprise Edition scales to very high performance levels required to support the largest enterprise online transaction processing (OLTP), highly complex data analysis, data warehousing systems, and Web sites.
SQL Server 2005 Standard Edition
SQL Server 2005 Standard Edition is best suited for small and medium sized organizations. It scales to meet reasonable volume and load of data.
SQL Server 2005 Workgroup Edition
SQL Server 2005 Workgroup Edition is the data management solution for small organizations that need a database with no limits on size or number of users.
SQL Server 2005 Developer Edition
SQL Server 2005 Developer Edition has all features of Enterprise edition, but it is licensed to use only for development and testing purposes and not for deployment on production systems.
SQL Server 2005 Express Edition
The SQL Server Express edition is a replacement for the MSDE (free database system). This edition is based on SQL Server 2005 and offers a lot more features than MSDE. Even though Microsoft claims that is edition can be used only for small applications, a smart design and appropriate caching will make this a smart choice for several types of applications. Several websites have switched from MS Access or MySql to SQL Server 2005 Express since it is free and offers lot of features of SQL Server 2005.
SQL Server Express is free and can be redistributed (subject to some agreement), and functions as the client database, as well as a basic server database. SQL Server Express is an ideal choice for deploying with small client-server applications as well as small web sites.
SQL Server 2005 Compact Edition
SQL Server Compact Edition is the compact database server for smart devices. SQL Server Compact Edition is capable of replicating data with SQL Server 2005 and SQL Server 2000.
SQL Server 2005 Runtime Edition
SQL Server 2005 Runtime Edition is a special edition designed for Microsoft ISV partners. Under the end user license agreement for SQL Server 2005 Runtime Edition, an independent software vendor (ISV) may embed SQL Server code into their software but end users are not allowed to use this instance of SQL Server to access from any other applications.
Among various versions mentioned above, SQL Server 2005 Expression is the only free version. Enterprise and standard editions can cost several thousand dollars depending on the number of users and number of CPUs in the system.