ILSpy is the open-source .NET assembly browser and decompiler.

Features

• Decompilation to C#
• Whole-project decompilation (csproj, not sln!)
• Search for types/methods/properties (substring)
• Hyperlink-based type/method/property navigation
• Base/Derived types navigation, history
• BAML to XAML decompiler
• Extensible via plugins (MEF)
• Check out the language support status