不错的级联菜单

大学： <select id="s1" name="s1"></select>
       <select id="s2" name="s2"></select>
       <select id="s3" name="s3"></select>
       <select id="s4" name="s4"></select>

对应js



<script language="JavaScript">
<!--
function LianDong(arr, sel)
{
var me = this;
this.$ = function(o)
{
  return document.getElementById(o);
}
this.sub = function (i, pid)
{
  for (var j=i+1; j<sel.length; j++)
  {
   me.$(sel[j]).length = 0;
   me.$(sel[j]).options[0] = new Option("请选择", "");
  }
  for ( var j = 0; j < arr.length; j++)
  {
   if (arr[j][1] == pid)
   {
    me.$(sel).options[me.$(sel).length] = new Option(arr[j][2], arr[j][0]);
   }
  }
}
this.init = function()
{
  me.sub(-1,"root");
  for (var i=0; i<sel.length-1; i++)
  {
   me.$(sel).onchange = function()
   {
    var i;
    for (i=0; me.$(sel)!=this; i++);
    me.sub(i, me.$(sel).value);
   }
  }
}
this.init();
}
var array=new Array();
array[0]=new Array("新疆","root","新疆");
array[1]=new Array("昌吉","新疆","昌吉");
array[2]=new Array("乌鲁木齐","新疆","乌鲁木齐");
array[3]=new Array("石河子","新疆","石河子");
array[4]=new Array("徐家汇","上海","徐家汇");
array[5]=new Array("新疆大学","乌鲁木齐","新疆大学");
array[6]=new Array("石河子大学","石河子","石河子大学");
array[7]=new Array("乌鲁木齐职业大学","乌鲁木齐","乌鲁木齐职业大学");
array[8]=new Array("信息工程学院","乌鲁木齐职业大学","信息工程学院");
array[9]=new Array("人文学院","乌鲁木齐职业大学","人文学院");
array[10]=new Array("昌吉职业学院","昌吉","昌吉职业学院");
array[11]=new Array("计算机系","昌吉职业学院","计算机系");
array[12]=new Array("机械系","昌吉职业学院","机械系");
array[13]=new Array("123","昌吉职业学院","123");
array[14]=new Array("甘肃","root","甘肃");
array[15]=new Array("兰州","甘肃","兰州");
array[16]=new Array("兰州大学","兰州","兰州大学");
array[17]=new Array("人文学院","兰州大学","人文学院");
array[18]=new Array("西藏","root","西藏");
array[19]=new Array("拉萨","西藏","拉萨");
array[20]=new Array("拉萨大学","拉萨","拉萨大学");
array[21]=new Array("佛学院","拉萨大学","佛学院");
var select = new Array("s1","s2","s3","s4");
var liandong=new LianDong(array, select)
//-->
</script>