This post is a list of useful resources for developers working with the 2007 Microsoft Office System and Visual Studio Tools for Office. It's not everything, not by a long chalk, but it's a start :-)
Custom Task Panes
http://channel9.msdn.com/ShowPost.aspx?PostID=197654
http://channel9.msdn.com/Showpost.aspx?postid=199933
Ribbon Extensibility
http://msdn.microsoft.com/office/tool/ribbon/
http://msdn2.microsoft.com/en-us/library/ms788199.aspx
http://channel9.msdn.com/Showpost.aspx?postid=208537
New File Format
http://msdn2.microsoft.com/en-us/library/ms406049.aspx
http://msevents.microsoft.com/cui/webcasteventdetails.aspx?eventid=1032304178&eventcategory=3&culture=en-us&countrycode=us
http://msdn2.microsoft.com/en-us/library/ms771890.aspx
http://blogs.msdn.com/brian_jones/default.aspx
http://channel9.msdn.com/showpost.aspx?postid=174061
Excel Services
http://msdn2.microsoft.com/en-us/library/ms517343.aspx
http://blogs.msdn.com/cumgranosalis/default.aspx