another-native-possibility.js

function clone( obj )
{
  function F(){}
  F.prototype = obj;
  return new F();
};

jQuery-clone.js

// See http://docs.jquery.com/Utilities/jQuery.extend
function clone( obj, deep )
{
  deep = deep || false;
  return deep ? jQuery.extend( true, {}, obj )
              : jQuery.extend( {}, obj );
}

native-clone.js

// Source: http://keithdevens.com/weblog/archive/2007/Jun/07/javascript.clone
function clone(obj){
  if ( obj == null ||
       typeof(obj) != 'object') { return obj; }

  var temp = new obj.constructor();
  for ( var key in obj )
  {
    temp[key] = clone( obj[key] );
  }
  return temp;
}

YUI-clone.js

YUI().use('json',function(Y){
  function clone( obj )
  {
    return Y.JSON.parse( Y.JSON.stringify( obj ) );
  }
});