Here is a list of links to posts on this blog that talk about extension methods:

• Extension Methods Part 1: An introduction to extension methods
• Extension Methods Part 2: Rules for consuming extension methods
• Extension Methods Part 3: Extension methods and byval / byref parameters
• Extension Methods Part 4: Extension methods and late binding
• Extension Methods Part 5: Generics and Extension Methods
• Extension Methods Part 6: Extension Methods Best Practices