Enterprise
SQL Server 2008 is a comprehensive data platform that meets the high demands of enterprise online transaction processing and data warehousing applications.
Standard
SQL Server 2008 Standard is a complete data management and business intelligence platform providing best-in-class ease of use and manageability for running departmental applications.
Workgroup
Run branch locations on this reliable data management and reporting platform that provides secure remote synchronization and management capabilities.
Compact
Available as a free download, build stand-alone and occasionally connected applications for mobile devices, desktops, and Web clients on all Microsoft Windows platforms.
Express
Available as a free download, Express is ideal for learning and building desktop and small server applications and for re-distribution by ISVs.
Enterprise and Standard Feature Compare (PDF)
Compact and Express Feature Compare (PDF)
Reference : Pinal Dave (https://blog.sqlauthority.com)