I can't believe I see more and more recent BizTalk implemenations in production WITHOUT SP1. With all the issues that we fixed in SP1, any new BizTalk Server 2004 project should simply never go into production without SP1. I can't stress that enough. The product team did phenomenal work raising the bar on the quality of this service pack. It can be downloaded here.
Additionally, I would also recommend that you contact premier support and ask for the following POST SP1 fixes, if you encounter any of the issues described below...which you undoubtedly will.