The release version of SQL Server 2005 Service Pack 1 is now available for download here. Books OnLine is here. While Database Mirroring is rightly getting most of the attention in this release, there are a number of enhancements and fixes which render this release worthy of your attention. Euan Garden offers a more extensive inventory here; there's also a pertinent KnowledgeBase article here, and the ReadMe for the installation here.
Now.. Go get it! 🙂