I use the approach found on the Enterprise jQuery site:

Here is their example showing how to declare private & public properties and functions. Everything is done as a self-executing anonymous function.

(function( skillet, $, undefined ) {
    //Private Property
    var isHot = true;

    //Public Property
    skillet.ingredient = "Bacon Strips";

    //Public Method
    skillet.fry = function() {
        var oliveOil;

        addItem( "\t\n Butter \n\t" );
        addItem( oliveOil );
        console.log( "Frying " + skillet.ingredient );
    };

    //Private Method
    function addItem( item ) {
        if ( item !== undefined ) {
            console.log( "Adding " + $.trim(item) );
        }
    }
}( window.skillet = window.skillet || {}, jQuery ));

So if you want to access one of the public members you would just go skillet.fry() or skillet.ingredients.

What's really cool is that you can now extend the namespace using the exact same syntax.

//Adding new Functionality to the skillet
(function( skillet, $, undefined ) {
    //Private Property
    var amountOfGrease = "1 Cup";

    //Public Method
    skillet.toString = function() {
        console.log( skillet.quantity + " " +
                     skillet.ingredient + " & " +
                     amountOfGrease + " of Grease" );
        console.log( isHot ? "Hot" : "Cold" );
    };
}( window.skillet = window.skillet || {}, jQuery ));

The third undefined argument

The third, undefined argument is the source of the variable of value undefined. I'm not sure if it's still relevant today, but while working with older browsers / JavaScript standards (ecmascript 5, javascript < 1.8.5 ~ firefox 4), the global-scope variable undefined is writable, so anyone could rewrite its value. The third argument (when not passed a value) creates a variable named undefined which is scoped to the namespace/function. Because no value was passed when you created the name space, it defaults to the value undefined.