SQL 2008 Express Editions and Service Packs -( from Microsoft site )

Microsoft® SQL Server® 2008 Express with Advanced Services 
Microsoft SQL Server2008 R2 RTM - Express with Advanced Services 
Microsoft SQL Server 2008 SP2 Express Edition Service Pack 2 

SQL Server 2005 Backward Compatibility-2


Microsoft® SQL Server® 2008 Express Edition Service Pack 1 
SQL Server 2005 Backward Compatibility-1

(Click on the option for download page in Microsoft Site)