C# Version Wise Features

C# 2.0
Generics Partial types Anonymous methods Iterators Nullable types Private setters (properties) Method group conversions (delegates)
C# 3.0
Implicitly typed local variables Object and collection initializers Auto-Implemented properties Anonymous types Extension methods Query expressions Lambda expressions Expression trees
C# 4.0 New features Whitepaper
Dynamic binding Named and optional arguments Generic co- and contravariance
C# 5.0 (planned)
Asynchronous methods Compiler as a service