I have been somewhat late on pointing to it yet here it is: a great 'informal' tool to help with BizTalk development as well as developing concepts through some great articles/brainstorming/tips&tricks/how-tos etc.
You can get the collection of articles and brainstorming in a .chm format Blogger's Guide to BizTalk workspace at GotDotNet. Alan Smith @ GotDotNet has been co-ordinating the effort to bring together BizTalk enthusiasts that blog avidly, resulting in the above.