ILSpy is the open-source .NET assembly browser and decompiler.
Development started after Red Gate announced that the free version of .NET Reflector would cease to exist by end of February 2011.
ILSpy requires the .NET Framework 4.0.
ILSpy Features
Assembly browsing
IL Disassembly
Support C# 5.0 "async"
Decompilation to C#
Supports lambdas and 'yield return'
Shows XML documentation
Decompilation to VB
Saving of resources
Save decompiled assembly as .csproj
Search for types/methods/properties (substring)
Hyperlink-based type/method/property navigation
Base/Derived types navigation
Navigation history
BAML to XAML decompiler
Save Assembly as C# Project
Find usage of field/method
Extensible via plugins (MEF)
Assembly Lists