Lutz Roeder's Reflector program uses the .NET Reflection API to navigate through .NET assemblies, list all the classes, and display everything about each class (methods, method parameters and return types, members, properties, and so on). It can even decompile .NET assemblies into readable C# code!

Reflector is an essential part of my .NET developer's toolbox. If you haven't used Reflector, download it now and start using it!