Simple comboboxes (manually editable selects) for jQuery/Bootstrap. Quick and dirty.

bootstrap-combobox.js

jQuery.fn.editableSelect = function () {
    var selects = $(this).filter('select');
    selects.each(function () {
        // Add an edit button to the select control, bootstrap style.
        var select = $(this);
        select.wrap('<div class="input-append" />');
        var editButton = $('<button class="btn" type="button" title="Enter your own value"><i class="icon-edit"></i></button>');
        select.parent().append(editButton);

        editButton.click(function () {
            // Replace the select element with a textbox.  Replace the edit button with a button that
            // takes the user back to the select. (original select is retained via closure)
            var wrapper = $(this).parent();
            wrapper.find('select, button').detach();

            var textbox = $('<input type="text" />').val(select.val());
            $.each(__editableSelectCopiedAttrs, function (index, value) {
                textbox.attr(value, select.attr(value));
            });
            wrapper.append(textbox);

            var revertButton = $('<button class="btn" type="button" title="Go back to select a value"><i class="icon-list"></i></button>');
            wrapper.append(revertButton);

            revertButton.click(function () {
                wrapper.find('input, button').remove();
                wrapper.append(select);
                wrapper.append(editButton);
            });
        });
    });
};
var __editableSelectCopiedAttrs = ['id', 'name', 'class'];