From aPress (links and text copied from aPress' Forthcoming Titles list):

Developing on Linux with C# and .NET: The Mono Project
By Daniel Solin
ISBN: 1-59059-117-8, 200 pages

The Mono Project is a complete implementation of Microsoft’s .NET technology in open source code. Developing on Linux with C# and .NET: The Mono Project gets you up to speed fast on this exciting technology and tells you everything you need to know to start developing today.
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This should be interesing to read and see what the author says about developing .NET apps on Linux. Nice to see that there is some traction with the Mono project to the point of having aPress publish a book on it.

Maximizing .NET Performance
By Nicholas J. Wienholt
ISBN: 1-59059-141-0, 200 pages

Maximizing .NET Performance focuses on providing developers and architects with the systematic analysis of performance relating to key Framework topics like remoting, garbage collection, and threading. Rather than a ‘tips and tricks’ approach, the book aims to provide a detailed exploration of each topic, and explore the ‘whys’ and ‘by how much’ aspects of performance that are often overlooked.
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Performance is one of my things. I love doing perf. testing and optimization of code. This book should be a ncie book to cover the techniques of doing this well with .NET and getting the most out of your .NET apps.

Web Services Security in the .NET Platform
By Peter Bromberg, Brian Nantz
ISBN: 1-59059-115-1, 450 pages

Web Services Security in the .NET Platform will be the comprehensive treatment on how to secure Web Services on the .NET Platform. Any company using .NET will eventually (if they haven’t already) be exposing part of their functionality as a .NET Web service and, given the times we live in, securing these features will become job number one.
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Another topic that I'm interested in... Should be interesting to see if the book covers WSE at all (it should).

Build Your Own .NET Language and Compiler
By Edward G. Nilges
ISBN: 1-59059-134-8, 600 pages

Virtually every experienced programmer today started out with some version of Basic or QuickBasic and has at some point in his or her career wondered how it worked. Build Your Own .NET Language and Compiler will teach language construction and design to .NET programmers, using a fully functioning “QuickBasic” compatible compiler as the example.
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Just a fun book in general. Hey, maybe I'll go and create Rob#. Or as my MSN Messenger by-line says: [tiësto#.net]!!! (fo those who are like, huh?, DJ Tiësto is by far the BEST DJ in the world and he's awesome!)

Code Generation in Microsoft .NET
By Kathleen Dollard
ISBN: 1-59059-137-2, 456 pages

Code Generation in Microsoft .NET teaches how to implement automatic code generation – a significant new trend in enterprise software development to reduce costs and improve efficiency and reliability.
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Should hopefully be a nice “under-the-covers“ style book. Always good to learn about how stuff actually works.