​

    jQuery.fn.filterByText = function(textbox, selectSingleMatch) {

        return this.each(function() {

            var select = this;

            var options = [];

            $(select).find('option').each(function() {

              options.push({value: $(this).val(), text: $(this).text(), className: $(this).attr('class')});

            });

            $(select).data('options', options);

            $(textbox).bind('change keyup', function() {

                var options = $(select).empty().data('options');

                var search = $(this).val().trim();

                var regex = new RegExp(search,"gi");

                $.each(options, function(i) {

                    var option = options[i];

                    if(option.text.match(regex) !== null) {

                        $(select).append(

                           $('<option>').text(option.text).val(option.value).addClass(option.className

                        );

                    }

                });

                if (selectSingleMatch === true && $(select).children().length === 1) {

                    $(select).children().get(0).selected = true;

                }

            });            

        });

    };

​

    $(function() {

        $('#select').filterByText($('#textbox'), true);

    });