Web Sites
BizTalk Developer Centre Homepage
Business Process Integration Patterns
Blogs
Cristoph Schittko's Blog http://blogs.xmladvice.com/christophdotnet/articles/879.aspx
Darren Jefford's Blog http://weblogs.asp.net/darrenj/
Darrell Norton's Blog http://dotnetjunkies.com/WebLog/darrell.norton/articles/9795.aspx
Charles Young Blog http://geekswithblogs.net/cyoung/
Martijn Hoogendoorn Blog http://martijnh.blogspot.com/
Gilles Zunino's Blog http://weblogs.asp.net/gzunino/
Keving Smith's Blog http://blogs.msdn.com/kevinsmi/
Arch Hacker's BizTalk Blog http://thearchhacker.blogspot.com/
BizTalk Server Stuff http://groups.msn.com/BizTalkServerStuff
Cristof Claissen's Blog http://weblogs.asp.net/christof_claessens/
BizTalk Core Engine Blog http://blogs.msdn.com/Biztalk_Core_Engine
Guy Barrette's Weblog http://weblogs.asp.net/guybarrette/
Scott Woodgate Blog http://weblogs.asp.net/scottwoo/
Jon Flanders Blog http://staff.develop.com/jfland
Richard Blewett's Blog http://www.dotnetconsult.co.uk/weblog
Books
Theres only one BizTalk 2004 book out as far as I know and thats BizTalk 2004 Unleashed
Newsgroups
The Microsoft BizTalk newsgroups on news.microsoft.com are a great resource