[.NET C#] Unified C# 3.0 Specification
The C# team at csharp-online.net has a download link for a consolidated document presenting the Unified C# 3.0 Specification, which brings together all prior C# specs with the latest version. It weighs in at slightly over 500 pages, but looks to be the most comprehensive documentation yet available for C#, and is an essential reference for any .NET developer working at the deeper levels.