Here’s a good read on the Design Patterns in use by .NET. 

It mentions the following patterns:

Ø      Observer Pattern

Ø      Iterator Pattern

Ø      Decorator Pattern

Ø      Adapter Pattern

Ø      Factory Pattern

Ø      Strategy Pattern

Ø      Composite Pattern

Ø      Template Method Pattern

Ø      Intercepting Filter Pattern

Ø      Page Controller Pattern