Here is a list of the basic software tools that I think every .Net Developer should have.  I use these on a regular basis.  I couldn't imagine developing without them.  As a far as third party add-ins, JetBrain's ReSharper is the best I have ever used.  You have to try it.  Also, I use BlogEngine.Net to document what my developers and I are doing on a regular basis.

Let me know if there are any other tools that I should add.

• Visual Studio 2005/2008 (MSDN Subscription)
• SQL 2005 Developer's Edition (MSDN Subscription)
• Visio 2007 (MSDN Subscription)
• Microsoft Office 2003/2007 (MSDN Subscription)
• Intellisense Snippets - C#
• Enterprise Library 3.x
• Enterprise Architect
• .Net 2.0, 3.0, 3.5
• Graphics Editor (Whatever you like)
• NUnit
• Resource Refactoring
• ReSharper
• VisualSVN
• TortoisesSVN
• Document X!
• DScribe 1.2!
• BlogEngine.Net
• Windows Live Writer
• Launchy
• Gladinet Cloud Desktop
• Flash Folder
• Internet Explorer 8
• Firefox
• Chrome

PS:  I try to keep this up-to-date.