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Essential books for a modern, professional .NET Developer...
By an Amazon.com customer
Refactoring: Improving the Design of Existing CodeRefactoring: Improving the Design of Existing Code by Martin Fowler
Buy new: $41.93 / Used from: $25.38
Learn to refactor as you code! Learn what Code Smells are and what to do abou them. (classic)
Design Patterns: Elements of Reusable Object-Oriented SoftwareDesign Patterns: Elements of Reusable Object-Oriented Software by Erich Gamma
Buy new: $31.25 / Used from: $21.32
Learn about the value of Design Patterns (classic)
Agile Software Development, Principles, Patterns, and PracticesAgile Software Development, Principles, Patterns, and Practices by Robert C. Martin
Buy new: $51.61 / Used from: $34.51
Learn pragmatic and essential principles of Software Development.
Agile Principles, Patterns, and Practices in C#Agile Principles, Patterns, and Practices in C# by Robert C. Martin
Buy new: $36.66 / Used from: $31.95
This looks like a great update to the classic, with an emphasis on C# instead of Java!
Refactoring to PatternsRefactoring to Patterns by Joshua Kerievsky
Buy new: $36.66 / Used from: $32.00
Learn how Design Patterns can help improve your design as you refactor.
Patterns of Enterprise Application ArchitecturePatterns of Enterprise Application Architecture by Martin Fowler
Buy new: $45.15 / Used from: $29.90
Learn about the most common application architectures, when they are appropriate and when they are not.
Refactoring Databases: Evolutionary Database DesignRefactoring Databases: Evolutionary Database Design by Scott W. Ambler
Buy new: $41.93 / Used from: $27.30
Inevitably you will need to touch data and fix poorly designed schemas. This is a great tool to help!
Test Driven Development: By ExampleTest Driven Development: By Example by Kent Beck
Buy new: $41.23 / Used from: $25.00
Learn Test Driven Design...
Code Complete: A Practical Handbook of Software ConstructionCode Complete: A Practical Handbook of Software Construction by Steve McConnell
Buy new: $31.49 / Used from: $21.99
Learn what a solid application should look like.
Coder to Developer: Tools and Strategies for Delivering Your SoftwareCoder to Developer: Tools and Strategies for Delivering Your Software by Mike Gunderloy
Buy new: $26.99 / Used from: $10.34
Don't know what you need to know? This is a good start...
Godel, Escher, Bach: An Eternal Golden BraidGodel, Escher, Bach: An Eternal Golden Braid by Douglas R. Hofstadter
Buy new: $15.61 / Used from: $6.85
Learn to see Patterns everywhere!
Death March (2nd Edition)Death March (2nd Edition) by Edward Yourdon
Buy new: $34.64 / Used from: $13.20
Learn to recognize symptoms of a failing project.
Beyond Code: Learn to Distinguish Yourself in 9 Simple Steps!Beyond Code: Learn to Distinguish Yourself in 9 Simple Steps! by Rajesh Setty
Buy new: $13.57 / Used from: $4.10
Learn the intangibles of being successful as a software developer.
Microsoft Windows Internals (4th Edition): Microsoft Windows Server 2003, Windows XP, and Windows 2000Microsoft Windows Internals (4th Edition): Microsoft Windows Server 2003, Windows XP, and Windows 2000 by Mark E. Russinovich
Buy new: $37.79 / Used from: $10.00
Learn what goes on in the dark depths of Windows. Learn to debug processes, threads, memory, etc.
C# Programming Language, The (2nd Edition)C# Programming Language, The (2nd Edition) by Anders Hejlsberg
Buy new: $44.99 / Used from: $5.00
Learn the C# Programming Language from its creator!
CLR via C#, Second Edition (Pro Developer)CLR via C#, Second Edition (Pro Developer) by Jeffrey Richter
Buy new: $37.79 / Used from: $24.46
Crawl inside the CLR and learn the answer to your questions of Why, How, What, etc...
The .NET Developer's Guide to Windows SecurityThe .NET Developer's Guide to Windows Security by Keith Brown
Buy new: $36.49 / Used from: $22.00
Embrace and take advantage of .NET and Windows Security features!
Programming Microsoft  ASP.NET 2.0 Core ReferenceProgramming Microsoft ASP.NET 2.0 Core Reference by Dino Esposito
Buy new: $34.99 / Used from: $0.87
Learn the essentials about ASP.NET 2.0
Programming Microsoft® ASP.NET 2.0 Applications: Advanced TopicsProgramming Microsoft® ASP.NET 2.0 Applications: Advanced Topics by Dino Esposito
Buy used from: $2.03
Learn the advanced essentials about ASP.NET 2.0
.NET Compact Framework Programming with C#.NET Compact Framework Programming with C# by Paul Yao
Buy new: $47.24 / Used from: $7.38
Got mobile?
Mastering Regular Expressions, Second EditionMastering Regular Expressions, Second Edition by Jeffrey E F Friedl
Buy used from: $7.32
NEVER EVER EVER EVER write a brute-force text-parser. Learn, Love, & Use Regex!
Cascading Style Sheets: The Definitive Guide, 2nd EditionCascading Style Sheets: The Definitive Guide, 2nd Edition by Eric A. Meyer
Buy used from: $2.88
A must for any web developer. (look for the 3rd ed coming in December '06)
Professional Ajax (Programmer to Programmer)Professional Ajax (Programmer to Programmer) by Nicholas C. Zakas
Buy used from: $0.29
Ajax, Atlas, XmlHttp, DHTML, JavaScript, its not new, but it sure is popular!
Agile Web Development with Rails: A Pragmatic Guide (Pragmatic Programmers)Agile Web Development with Rails: A Pragmatic Guide (Pragmatic Programmers) by Dave Thomas
Buy used from: $0.17
Learn another language & framework so you truly can grok .NET and its place in the world.