Saw some of these in someone else's blog post on soon to be released books and they spark my interest. Not sure if I'll ever find time to read them but I'll throw them here so at least they get on my radar:
Windows Internals: Including Windows Server 2008 and Windows Vista, Fifth Edition by Mark Russinovich and David Solomon (978-0735625303)
In my opinion a must-read cover-to-cover for every developer targeting the Windows platform. Sure enough, there will be chapters that are no more exciting than watching wet paint dry, but if you really want to know how the Windows OS is structured and how it all woks, this is the book to check out. Since its previous release it has grown over 200 pages with exciting new Vista/2008 Server stuff. Looking forward to it.
Concurrent Programming on Windows by Joe Duffy (978-0321434821)
With the new challenges arising from the multi/many-core wave, the art of writing concurrent applications has never been more important to master. This book explains the fundamentals of concurrent application development, best practices and more, targeting the Windows platform. Joe's been working on various concurrency APIs ranging from the .NET 2.0 thread pool to the Parallel Extensions to the .NET Framework.
Framework Design Guidelines: Conventions, Idioms, and Patterns for Reusable .NET Libraries (2nd Edition) by Krzysztof Cwalina and Brad Abrams (978-0321545619)
"Do, Don't, Consider and Avoid" are the four keywords of this book. If you want to learn how to structure and write reusable .NET libraries, there's no better book to look for than this one. With lots of annotations on applications within Microsoft by various architects, the book is not only a must-have reference, it's also well-suited to read cover-to-cover in a few evenings.