Overview of SharePoint and Office App development: http://msdn.microsoft.com/en-us/library/office/apps/jj220030
SharePoint 2013 Developer MSDN site at http://msdn.microsoft.com/en-us/library/jj163794(v=office.15)
Steve Fox’s blog (which shows how to integrate SharePoint and Windows Azure in more general ways) at http://blogs.msdn.com/steve_fox
Windows Azure Developer Portal at http://www.microsoft.com/windowsazure