SharePoint development patterns and practices

The Developing SharePoint Applications guidance helps architects and developers design and build applications that are both flexible and scaleable.
http://msdn.microsoft.com/en-us/library/dd203468.aspx

The TechNet best practice resource centre is another good resource.
http://technet.microsoft.com/en-us/office/sharepointserver/bb736746.aspx

Or checkout my SharePoint reading list:
http://delicious.com/paulabraham/sharepoint

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