Jon Jagger & Nigel Perry 
Annotated C# Standard [PDF ebook] 

Standards, while being definitive, do not usually serve as the best reference to the use of a programming language. Books on languages usually are able to explain usage better, but lack the definitive precision of a standard. Annotated C# Standard combines the two; it is the standard with added explanatory material. — Written by members of the standards committee- Annotates the standard with practical implementation advice- The definitive reference to the C# International Standard