SQL Server 2005 feature comparison by edition
You can find which editons of SQL Server 2005 have which feature @ https://www.microsoft.com/sql/2005/productinfo/sql2005features.asp
Essentially as you move from SQL 2005 Express edition through to SQL 2005 Enterprise edition you gain the features that give you scalability and high availablilty. Only Standard and Enterprise editions come with Integration Services and only the Enterprise edition comes with the new Report Builder application that enables end users to create their own reports.
Interestingly the Standard edition now comes with 2 node failover clustering and the new Database Mirroring capability.