Cutting to the chase: What's New in SQL Server 2005 SP3 http://msdn.microsoft.com/en-us/library/dd353312(SQL.90).aspx
Links etc...
SP3 (Std, Dev, Ent)
SP3 Express
SP3 Express Advanced
SP3 express Toolkit
SQL 2005 Feature Pack Refresh December 2008
SQL 2005 BOL Refresh
SQL 2005 SP3 Read Me