There are quite a lot of changes and enhancements in SQL Server 2005. Few of them are listed here :
=> Database Partitioning
=> Dynamic Management Views
=> System Catalog Views
=> Resource Database
=> Database Snapshots
=> SQL Server Integration Services
=> Support for Analysis Services on a  Fail over Cluster.
=> Profiler being able to trace the MDX queries of the Analysis Server.
=> Peer-toPeer Replication
=> Database Mirroring