If you haven't seen Reflector for .Net then go and check it out now: http://www.aisto.com/roeder/dotnet/ - it is a great tool.
"Reflector is a class browser for .NET components. It supports assembly and namespace views, type and member search, XML documentation, call and callee graphs, IL, Visual Basic, Delphi and C# decompiler, dependency trees, base type and derived type hierarchies and resource viewers."
I've been using Reflector for some time, but I have only just come across the add-ins you can use to extend it (including a diff tool, dependency graphs, and VS integration). Have a look at them here:
http://csharp21.tripod.com/ReflectorAddIns/