BizTalk Server 2004 launches today. The launch event is to be held in Mountain View, CA. If you aren't able to attend, it will be archived at http://www.microsoft.com/biztalk.
Evaluation version is available here.
For additional press releases *after* the launch (12:30PM PST), please visit here.
Also, check out the upcoming MSDN webcasts for BizTalk Server 2004.