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