C# Language Enhancement
C# 3,0 LINQ
C# 3.0 and LINQ With Language Extention
C# Dynamic Language Enhancement
C# 4.0 can be found on the Downloads page. The CSharpDynamic samples include several projects showing how to use Dynamic with Office, IronPython and other technologies. There is also a covariance and contravariance example, and an example show how to use the new IDynamicObject interface to create native C# objects that can be called dynamically.
The document New Features in C# 4.0 is a high level description of the additions to the C# language, and the samples are designed to show off the new language features, particularly around the dynamic scenario.