Over the years Microsoft is releasing Patterns and Practices books and distributing them for free. I think this one as great community effort and is continue to evolve. When I started writing code in .NET I always used to carry them with me. You cannot ask for more if you have them with you.
In its home page at MSDN you will find the structure http://msdn.microsoft.com/en-us/library/ms998572.aspx
There are a few to come along with revisions and can be found at http://msdn.microsoft.com/en-us/practices/bb232643.aspx
Few HOT releases in 2009 are
Composite Application Guidance for WPF and Silverlight (October 2009) The Composite Application Guidance for WPF and Silverlight is designed to help you more easily build enterprise-level Windows Presentation Foundation (WPF) and Silverlight client applications. This guidance will help you design and build flexible composite client applications.
Microsoft Application Architecture Guide: 2nd Edition (October 2009) The guide is intended to help developers and solution architects design and build effective, high quality applications using the Microsoft platform and the .NET Framework more quickly and with less risk; it provides guidance for using architecture principles, design principles, and patterns that are tried and trusted. The guidance is presented in sections that correspond to major architecture and design focus points. It is designed to be used as a reference resource or to be read from beginning to end. This guide is also available as a book from Microsoft Press (ISBN 9780735627109)
Developing SharePoint Applications (August 2009) This guidance helps solution architects and software developers build applications using SharePoint. The guide covers areas such as fundamental design and development decisions, enterprise qualities, flexible content oriented approaches, and LOB integration. It provides reusable components to help with logging, repositories, configuration, service location, and event driven site creation. Two reference implementations demonstrate a partner extranet (using MOSS) and a training management application (using WSS).
The complete catalog can be found at http://msdn.microsoft.com/en-us/practices/bb190351.aspx.
List of guides which are not valid at http://msdn.microsoft.com/en-us/practices/bb190351.aspx#Retired