Lutz's Reflector, Anakrino and the power of decompilation
I've been a long time fan of Anakrino. This belongs to the amazing genre of .NET "decompilers"... it takes MSIL and turns it back into C#. Amazingly useful for discovering what's actually going on in those Framework classes when you can't quite solve those tricky problems.
My toolkit has always had Anakrino and Lutz Roeders Reflector for .NET, but now I may not need Anakrino because Lutz has put simliar decompilation functionality into Reflector. The twist - Reflector can do VB .NET as well as C#.