Office 2003 SP1 was released on July 27, 2004. You can download it here.
In addition to bug fixes, SP1 delivers advances in several key areas:
As a heavy user of both OneNote and InfoPath, it is amazing how many great features were added to this release based directly from customer requests. On his Weblog, Chris Pratley has done a great job of opening a dialog with OneNote users to solicit feedback on future product releases, and explaining why certain decisions were made. I think this is an exciting new way of guiding product development.