Two books I have been reading lately are by Bill Wagner and they are an excellent C# resource all .NET developers should have lying around near their desk:
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Effective C#
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More Effective C#
These are a great resource to let you become a "better than average" C# programmer. Out of interest, I just found a link with the contents of the first book here. As always, if you like what you see I would recommend getting a copy of both.