What is the best or most interesting use of Extension Methods you've seen? [closed]

Answer 1

I am converting a lot of Java to C#. Many of the methods vary only in capitalization or other small syntax differences. So Java code such as

myString.toLowerCase();

will not compile but by adding an extension method

public static void toLowerCase(this string s)
{
    s.ToLower();
}

I can catch all the methods (and I assume a good compiler will inline this anyway?).

It's certainly made the job much easier and more reliable. (I thank @Yuriy - see answer in: differences between StringBuilder in Java and C#) for the suggestion.