The feature pack for SQL Server 2005 is available for download here.

The feature pack is a collection of useful SQL Server 2005 components.  Some of them are the redistributable portions of SQL Server 2005 (for example, you can download SQLCMD so that you can use it with SQL Server 2000 and 7.0).  Others are cool add-ons (windows forms controls for viewing data mining models, OLEDB driver for DB2, a preview of an integration services component for mySAP).

-David