Here's the list of books my company is planning to buy in the next few days (suggestions are welcome) :

Windows Forms Programming in C#

Essential .NET, Volume I: The Common Language Runtime

Patterns of Enterprise Application Architecture 

Programming Windows with C# (Core Reference)

.NET Framework Security

Microsoft ADO.NET (Core Reference)

Programming .NET Components

Transactional COM+: Building Scalable Applications

About Face 2.0: The Essentials of Interaction Design

Shared Source CLI Essentials

How to Break Software: A Practical Guide to Testing

.NET and COM: The Complete Interoperability Guide

Pair Programming Illuminated

Streamlined Object Modeling: Patterns, Rules, and Implementation

PeopleWare

Managing Software Requirements