I am very excited about the new BDC book that is coming out soon from SharePoint Pod Show co-hosts Brett Lonsdale and Nick Swan called "SharePoint 2007 Developer's Guide to the BDC". I have had a chance to review some of the chapters in this book and am very excited to see something like this hit the market.
You can check out the details of the book at the following link as well as pre-order a copy.
http://www.manning.com/lonsdale