Here are a number of additional resources that you might find useful. Also note that some of the chapters offer more resources in sections called Further Reading, which are specific to the material covered in those chapters.
OBA Central: www.obacentral.com
MSDN OBA Developer Portal: http://msdn.microsoft.com/oba
MSDN Office Developer How-To Center: http://msdn2.microsoft.com/en-us/office/bb266408.aspx
Office Developer Center: http://msdn2.microsoft.com/en-us/office/default.aspx
Visual Studio Tools for Office Developer Center: http://msdn2.microsoft.com/en-us/office/aa905533.aspx
Excel Services Information Center Portal on MSDN: http://msdn2.microsoft.com/en-us/office/bb203828.aspxv
Ribbon User Interface: http://msdn.microsoft.com/office/tool/ribbon/default.aspx
XML File Formats: http://msdn.microsoft.com/office/tool/xml/2007/default.aspx
Business Data Catalog Information Center: http://msdn2.microsoft.com/en-us/office/bb251754.aspx
Business Data Catalog Software Development Kit: http://msdn2.microsoft.com/en-us/library/ms563661.aspx
Introduction to Content Types: http://office.microsoft.com/en-us/sharepointserver/HA101495511033.aspx?pid=CH101779691033
Content Types Software Development Kit: http://msdn2.microsoft.com/en-us/library/ms479905.aspx
Microsoft Office SharePoint Server 2007 Software Development Kit: http://msdn2.microsoft.com/en-us/library/ms550992.aspx
Office Developer Webcasts: http://www.microsoft.com/events/series/officedeveloperlive.mspx
How Do I? Screencasts: http://msdn.microsoft.com/office/learn/screencasts
Building Office Business Applications:
Brian Randell’s blog, for information about SQL Server, Microsoft Office, and Visual Studio Tools for Office (VSTO): http://sqljunkies.com/WebLog/brianr/
Eric Carter’s blog, for information about Microsoft Office and VSTO: http://blogs.msdn.com/eric_carter/
Microsoft Office fluent interface: http://blogs.msdn.com/jensenh/
Office Developers: http://blogs.msdn.com/erikaehrli/
Open XML File Formats:
Paul Stubbs’ blog, for information about Microsoft Office, VSTO, and OBAs: http://blogs.msdn.com/pstubbs/
Scott Guthrie’s blog, for information on a variety of topics: http://weblogs.asp.net/scottgu/
SharePoint Products and Technologies:
Visual Studio extensions for SharePoint and SharePoint Designer: http://blogs.msdn.com/alexma/
6 Microsoft Office Business Applications for Microsoft SharePoint Server 2007 by Rob Barker, Joanna Bichsel, Adam Buenz, Steve Fox, John Holliday, Bhushan Nene, and Karthik Ravindran (Microsoft Press)
Microsoft Office SharePoint Server Best Practices by Ben Curry, Bill English, and Mark Schneider (Microsoft Press)
Inside Microsoft Windows SharePoint Services 3.0 by Ted Pattison and Daniel Larson (Microsoft Press)
VSTO for Mere Mortals: A VBA Developer’s Guide to Microsoft Office Development Using Visual Studio 2005 Tools for Office by Kathleen McGrath and Paul Stubbs (Addison-Wesley Professional)
Visual Studio Tools for Office by Eric Carter and Eric Lippert (Addison-Wesley Professional)