$.maxZIndex = $.fn.maxZIndex = function (opt) {
    /// <summary>
    /// Returns the max zOrder in the document (no parameter)
    /// Sets max zOrder by passing a non-zero number
    /// which gets added to the highest zOrder.
    /// </summary>    
    /// <param name="opt" type="object">
    /// inc: increment value, 
    /// group: selector for zIndex elements to find max for
    /// </param>
    /// <returns type="jQuery" />
    var def = { inc: 10, group: "*" };
    $.extend(def, opt);
    var zmax = 0;
    $(def.group).each(function () {
        var cur = parseInt($(this).css('z-index'));
        zmax = cur > zmax ? cur : zmax;
    });
    if (!this.jquery)
        return zmax;

    return this.each(function () {
        zmax += def.inc;
        $(this).css("z-index", zmax);
    });
}

$(function () {
    $("#menu > li").hover(
        function () {
            //$(this).find(".sub_menu").css("display", "block");
            $(this).find(".sub_menu").slideDown(200).delay(30);
        },
        function () {
            //$(this).find(".sub_menu").css("display", "none");
            $(this).find(".sub_menu").slideUp(200);
        });
});