We're using the SQL Server 2005 Service Broker functionality to replicate data and send messages between databases, and we got a tip from a Microsoftie to get hold of this book.
The book is written by Roger Wolter, Program Manager on the Service Broker team and it is straight forward, full of samples starting with a really, really simple service broker sample and builds up throughout the book. It covers most things you need to know about the topic, poison messages, multiple servers, certificates etc. and everything within some 220 pages.
Cross-posted from my blog at http://weblogs.asp.net/jdanforth