Which class hierarchy is most necessary in order to get an excellent grasp of C#, for the aspiring C# desktop applications programmer? Not just the totally obvious stuff.
EDIT: To clarify, I mean, that as I am learning C#, I would like to know what are the classes I should be acquainted with, which aren’t necessarily going to be obvious to someone who isn’t experienced enough to know what is, and is not important to learn.
EDIT2: Are there any more obscure classes? So far I know a good deal about many of these already given.
Just found this link in another thread: map
Also, download Reflector and browse through the .NET Framework classes, starting with mscorlib.dll and System.dll.