Okay this is probably going to be old news for anyone reading this but...
BizTalk Documenter - Document your code
http://www.codeplex.com/BizTalkDocumenter
BizUnit - Test your code
http://www.codeplex.com/bizunit
BizTalk Orchestration Profiler - Useful for code coverage when used with BizUnit
http://www.codeplex.com/BiztalkOrcProfiler
I am doing a lot of refactoring (Unit Test and Profiling a must to check for code breaks) on an inherited BizTalk solution - so far I have replaced 40% (target is 90%) of the orchestrations with simple web services and removed some really complicated maps (a big performance drain) by getting SQL to produce the documents in the correct XML format rather than use a different format and then transforming it. Using the documentation tool to check for unused maps.
As I write this up - I find a better post with even more referenced goodies - http://geekswithblogs.net/benny/archive/2007/06/14/113218.aspx