比较好的二级联动:

<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN">
<HTML>
<HEAD>
<TITLE> New Document </TITLE>
<META NAME="Generator" CONTENT="EditPlus">
<META NAME="Author" CONTENT="">
<META NAME="Keywords" CONTENT="">
<META NAME="Description" CONTENT="">

<script language="javascript" type="text/javascript">
provinceArray = new Array("北京市","上海市","天津市","重庆市","河北省","山西省","内蒙古自治区","辽宁省","吉林省","黑龙江省","江苏省","浙江省","安徽省","福建省","江西省","山东省","河南省","湖北省","湖南省","广东省","广西壮族自治区","海南省","四川省","贵州省","云南省","西藏自治区","陕西省","甘肃省","宁夏回族自治区","青海省","新疆维吾尔族自治区","香港特别行政区","澳门特别行政区","台湾省","其它");

//定义 城市 数据数组
cityArray = new Array(); 
cityArray[0] = new Array("北京市","东城|西城|崇文|宣武|朝阳|丰台|石景山|海淀|门头沟|房山|通州|顺义|昌平|大兴|平谷|怀柔|密云|延庆"); 
cityArray[1] = new Array("上海市","黄浦|卢湾|徐汇|长宁|静安|普陀|闸北|虹口|杨浦|闵行|宝山|嘉定|浦东|金山|松江|青浦|南汇|奉贤|崇明"); 
cityArray[2] = new Array("天津市","和平|东丽|河东|西青|河西|津南|南开|北辰|河北|武清|红挢|塘沽|汉沽|大港|宁河|静海|宝坻|蓟县"); 
cityArray[3] = new Array("重庆市","万州|涪陵|渝中|大渡口|江北|沙坪坝|九龙坡|南岸|北碚|万盛|双挢|渝北|巴南|黔江|长寿|綦江|潼南|铜梁 |大足|荣昌|壁山|梁平|城口|丰都|垫江|武隆|忠县|开县|云阳|奉节|巫山|巫溪|石柱|秀山|酉阳|彭水|江津|合川|永川|南川"); 
cityArray[4] = new Array("河北省","石家庄|邯郸|邢台|保定|张家口|承德|廊坊|唐山|秦皇岛|沧州|衡水"); 
cityArray[5] = new Array("山西省","太原|大同|阳泉|长治|晋城|朔州|吕梁|忻州|晋中|临汾|运城"); 
cityArray[6] = new Array("内蒙古自治区","呼和浩特|包头|乌海|赤峰|呼伦贝尔盟|阿拉善盟|哲里木盟|兴安盟|乌兰察布盟|锡林郭勒盟|巴彦淖尔盟|伊克昭盟"); 
cityArray[7] = new Array("辽宁省","沈阳|大连|鞍山|抚顺|本溪|丹东|锦州|营口|阜新|辽阳|盘锦|铁岭|朝阳|葫芦岛"); 
cityArray[8] = new Array("吉林省","长春|吉林|四平|辽源|通化|白山|松原|白城|延边"); 
cityArray[9] = new Array("黑龙江省","哈尔滨|齐齐哈尔|牡丹江|佳木斯|大庆|绥化|鹤岗|鸡西|黑河|双鸭山|伊春|七台河|大兴安岭"); 
cityArray[10] = new Array("江苏省","南京|镇江|苏州|南通|扬州|盐城|徐州|连云港|常州|无锡|宿迁|泰州|淮安"); 
cityArray[11] = new Array("浙江省","杭州|宁波|温州|嘉兴|湖州|绍兴|金华|衢州|舟山|台州|丽水"); 
cityArray[12] = new Array("安徽省","合肥|芜湖|蚌埠|马鞍山|淮北|铜陵|安庆|黄山|滁州|宿州|池州|淮南|巢湖|阜阳|六安|宣城|亳州"); 
cityArray[13] = new Array("福建省","福州|厦门|莆田|三明|泉州|漳州|南平|龙岩|宁德"); 
cityArray[14] = new Array("江西省","南昌市|景德镇|九江|鹰潭|萍乡|新馀|赣州|吉安|宜春|抚州|上饶"); 
cityArray[15] = new Array("山东省","济南|青岛|淄博|枣庄|东营|烟台|潍坊|济宁|泰安|威海|日照|莱芜|临沂|德州|聊城|滨州|菏泽"); 
cityArray[16] = new Array("河南省","郑州|开封|洛阳|平顶山|安阳|鹤壁|新乡|焦作|濮阳|许昌|漯河|三门峡|南阳|商丘|信阳|周口|驻马店|济源"); 
cityArray[17] = new Array("湖北省","武汉|宜昌|荆州|襄樊|黄石|荆门|黄冈|十堰|恩施|潜江|天门|仙桃|随州|咸宁|孝感|鄂州");
cityArray[18] = new Array("湖南省","长沙|常德|株洲|湘潭|衡阳|岳阳|邵阳|益阳|娄底|怀化|郴州|永州|湘西|张家界"); 
cityArray[19] = new Array("广东省","广州|深圳|珠海|汕头|东莞|中山|佛山|韶关|江门|湛江|茂名|肇庆|惠州|梅州|汕尾|河源|阳江|清远|潮州|揭阳|云浮"); 
cityArray[20] = new Array("广西壮族自治区","南宁|柳州|桂林|梧州|北海|防城港|钦州|贵港|玉林|南宁地区|柳州地区|贺州|百色|河池"); 
cityArray[21] = new Array("海南省","海口|三亚"); 
cityArray[22] = new Array("四川省","成都|绵阳|德阳|自贡|攀枝花|广元|内江|乐山|南充|宜宾|广安|达川|雅安|眉山|甘孜|凉山|泸州"); 
cityArray[23] = new Array("贵州省","贵阳|六盘水|遵义|安顺|铜仁|黔西南|毕节|黔东南|黔南"); 
cityArray[24] = new Array("云南省","昆明|大理|曲靖|玉溪|昭通|楚雄|红河|文山|思茅|西双版纳|保山|德宏|丽江|怒江|迪庆|临沧");
cityArray[25] = new Array("西藏自治区","拉萨|日喀则|山南|林芝|昌都|阿里|那曲"); 
cityArray[26] = new Array("陕西省","西安|宝鸡|咸阳|铜川|渭南|延安|榆林|汉中|安康|商洛"); 
cityArray[27] = new Array("甘肃省","兰州|嘉峪关|金昌|白银|天水|酒泉|张掖|武威|定西|陇南|平凉|庆阳|临夏|甘南"); 
cityArray[28] = new Array("宁夏回族自治区","银川|石嘴山|吴忠|固原"); 
cityArray[29] = new Array("青海省","西宁|海东|海南|海北|黄南|玉树|果洛|海西"); 
cityArray[30] = new Array("新疆维吾尔族自治区","乌鲁木齐|石河子|克拉玛依|伊犁|巴音郭勒|昌吉|克孜勒苏柯尔克孜|博尔塔拉|吐鲁番|哈密|喀什|和田|阿克苏"); 
cityArray[31] = new Array("香港特别行政区","香港特别行政区"); 
cityArray[32] = new Array("澳门特别行政区","澳门特别行政区"); 
cityArray[33] = new Array("台湾省","台北|高雄|台中|台南|屏东|南投|云林|新竹|彰化|苗栗|嘉义|花莲|桃园|宜兰|基隆|台东|金门|马祖|澎湖"); 
cityArray[34] = new Array("其它","北美洲|南美洲|亚洲|非洲|欧洲|大洋洲");

function initProvince(){
document.all.selProvince.length = 0 ; 
for(i=0; i<provinceArray.length; i++){
   document.all.selProvince.options[i] = new Option(provinceArray[i],provinceArray[i]);
}
getCity(document.all.selProvince.options[0].value)
}

function getCity(currProvince)
{
    //当前 所选择 的 省
    var currProvince = currProvince;
    var i,j,k;
    //清空 城市 下拉选单
    document.all.selCity.length = 0 ; 
    for (i = 0 ;i <cityArray.length;i++)
      {   
          //得到 当前省 在 城市数组中的位置
          if(cityArray[i][0]==currProvince)
            {   
                //得到 当前省 所辖制的 地市
                tmpcityArray = cityArray[i][1].split("|")
                  for(j=0;j<tmpcityArray.length;j++)
                  {
                    //填充 城市 下拉选单
                    document.all.selCity.options[document.all.selCity.length] = new Option(tmpcityArray[j],tmpcityArray[j]); 
                  }
            } 
      } 
}
</script>

</HEAD>

<BODY onload="initProvince()">
选择省市:
		<select name="province" id="selProvince" onChange = "getCity(this.options[this.selectedIndex].value)">
    	</select>
    	<select name="city" id="selCity">
        	<option>北京</option>
    	</select>
</BODY>
</HTML>




二级联动:



<html>
<head> 
<title></title>
<meta http-equiv="Content-Type" content="text/html; charset=gb2312">
</head>
<body bgcolor=#FFFFFF alink=#333333 vlink=#333333 link=#333333 topmargin=0 leftmargin=0>
<form action="http://www.chinaleader.com/cgi-bin/register.cgi" method=post name="creator" enctype="multipart/form-data">
<script language="javascript">
<!--
var where = new Array(35); 
function comefrom(loca,locacity) { this.loca = loca; this.locacity = locacity; } 
where[0]= new comefrom("请选择省份名","请选择城市名");
where[1] = new comefrom("北京","|东城|西城|崇文|宣武|朝阳|丰台|石景山|海淀|门头沟|房山|通州|顺义|昌平|大兴|平谷|怀柔|密云|延庆"); 
where[2] = new comefrom("上海","|黄浦|卢湾|徐汇|长宁|静安|普陀|闸北|虹口|杨浦|闵行|宝山|嘉定|浦东|金山|松江|青浦|南汇|奉贤|崇明"); 
where[3] = new comefrom("天津","|和平|东丽|河东|西青|河西|津南|南开|北辰|河北|武清|红挢|塘沽|汉沽|大港|宁河|静海|宝坻|蓟县"); 
where[4] = new comefrom("重庆","|万州|涪陵|渝中|大渡口|江北|沙坪坝|九龙坡|南岸|北碚|万盛|双挢|渝北|巴南|黔江|长寿|綦江|潼南|铜梁|大足|荣昌|壁山|梁平|城口|丰都|垫江|武隆|忠县|开县|云阳|奉节|巫山|巫溪|石柱|秀山|酉阳|彭水|江津|合川|永川|南川"); 
where[5] = new comefrom("河北","|石家庄|邯郸|邢台|保定|张家口|承德|廊坊|唐山|秦皇岛|沧州|衡水"); 
where[6] = new comefrom("山西","|太原|大同|阳泉|长治|晋城|朔州|吕梁|忻州|晋中|临汾|运城"); 
where[7] = new comefrom("内蒙古","|呼和浩特|包头|乌海|赤峰|呼伦贝尔盟|阿拉善盟|哲里木盟|兴安盟|乌兰察布盟|锡林郭勒盟|巴彦淖尔盟|伊克昭盟"); 
where[8] = new comefrom("辽宁","|沈阳|大连|鞍山|抚顺|本溪|丹东|锦州|营口|阜新|辽阳|盘锦|铁岭|朝阳|葫芦岛"); 
where[9] = new comefrom("吉林","|长春|吉林|四平|辽源|通化|白山|松原|白城|延边"); 
where[10] = new comefrom("黑龙江","|哈尔滨|齐齐哈尔|牡丹江|佳木斯|大庆|绥化|鹤岗|鸡西|黑河|双鸭山|伊春|七台河|大兴安岭"); 
where[11] = new comefrom("江苏","|南京|镇江|苏州|南通|扬州|盐城|徐州|连云港|常州|无锡|宿迁|泰州|淮安"); 
where[12] = new comefrom("浙江","|杭州|宁波|温州|嘉兴|湖州|绍兴|金华|衢州|舟山|台州|丽水"); 
where[13] = new comefrom("安徽","|合肥|芜湖|蚌埠|马鞍山|淮北|铜陵|安庆|黄山|滁州|宿州|池州|淮南|巢湖|阜阳|六安|宣城|亳州"); 
where[14] = new comefrom("福建","|福州|厦门|莆田|三明|泉州|漳州|南平|龙岩|宁德"); 
where[15] = new comefrom("江西","|南昌市|景德镇|九江|鹰潭|萍乡|新馀|赣州|吉安|宜春|抚州|上饶"); 
where[16] = new comefrom("山东","|济南|青岛|淄博|枣庄|东营|烟台|潍坊|济宁|泰安|威海|日照|莱芜|临沂|德州|聊城|滨州|菏泽"); 
where[17] = new comefrom("河南","|郑州|开封|洛阳|平顶山|安阳|鹤壁|新乡|焦作|濮阳|许昌|漯河|三门峡|南阳|商丘|信阳|周口|驻马店|济源"); 
where[18] = new comefrom("湖北","|武汉|宜昌|荆州|襄樊|黄石|荆门|黄冈|十堰|恩施|潜江|天门|仙桃|随州|咸宁|孝感|鄂州");
where[19] = new comefrom("湖南","|长沙|常德|株洲|湘潭|衡阳|岳阳|邵阳|益阳|娄底|怀化|郴州|永州|湘西|张家界"); 
where[20] = new comefrom("广东","|广州|深圳|珠海|汕头|东莞|中山|佛山|韶关|江门|湛江|茂名|肇庆|惠州|梅州|汕尾|河源|阳江|清远|潮州|揭阳|云浮"); 
where[21] = new comefrom("广西","|南宁|柳州|桂林|梧州|北海|防城港|钦州|贵港|玉林|南宁地区|柳州地区|贺州|百色|河池"); 
where[22] = new comefrom("海南","|海口|三亚"); 
where[23] = new comefrom("四川","|成都|绵阳|德阳|自贡|攀枝花|广元|内江|乐山|南充|宜宾|广安|达川|雅安|眉山|甘孜|凉山|泸州"); 
where[24] = new comefrom("贵州","|贵阳|六盘水|遵义|安顺|铜仁|黔西南|毕节|黔东南|黔南"); 
where[25] = new comefrom("云南","|昆明|大理|曲靖|玉溪|昭通|楚雄|红河|文山|思茅|西双版纳|保山|德宏|丽江|怒江|迪庆|临沧");
where[26] = new comefrom("西藏","|拉萨|日喀则|山南|林芝|昌都|阿里|那曲"); 
where[27] = new comefrom("陕西","|西安|宝鸡|咸阳|铜川|渭南|延安|榆林|汉中|安康|商洛"); 
where[28] = new comefrom("甘肃","|兰州|嘉峪关|金昌|白银|天水|酒泉|张掖|武威|定西|陇南|平凉|庆阳|临夏|甘南"); 
where[29] = new comefrom("宁夏","|银川|石嘴山|吴忠|固原"); 
where[30] = new comefrom("青海","|西宁|海东|海南|海北|黄南|玉树|果洛|海西"); 
where[31] = new comefrom("新疆","|乌鲁木齐|石河子|克拉玛依|伊犁|巴音郭勒|昌吉|克孜勒苏柯尔克孜|博尔塔拉|吐鲁番|哈密|喀什|和田|阿克苏"); 
where[32] = new comefrom("香港",""); 
where[33] = new comefrom("澳门",""); 
where[34] = new comefrom("台湾","|台北|高雄|台中|台南|屏东|南投|云林|新竹|彰化|苗栗|嘉义|花莲|桃园|宜兰|基隆|台东|金门|马祖|澎湖"); 
where[35] = new comefrom("其它","|北美洲|南美洲|亚洲|非洲|欧洲|大洋洲"); 
function select() {
with(document.creator.province) { var loca2 = options[selectedIndex].value; }
for(i = 0;i < where.length;i ++) {
if (where[i].loca == loca2) {
loca3 = (where[i].locacity).split("|");
for(j = 0;j < loca3.length;j++) { with(document.creator.city) { length = loca3.length; options[j].text = loca3[j]; options[j].value = loca3[j]; var loca4=options[selectedIndex].value;}}
break;
}}
document.creator.newlocation.value=loca2+loca4;
}
function init() {
with(document.creator.province) {
length = where.length;
for(k=0;k<where.length;k++) { options[k].text = where[k].loca; options[k].value = where[k].loca; }
options[selectedIndex].text = where[0].loca; options[selectedIndex].value = where[0].loca;
}
with(document.creator.city) {
loca3 = (where[0].locacity).split("|");
length = loca3.length;
for(l=0;l<length;l++) { options[l].text = loca3[l]; options[l].value = loca3[l]; }
options[selectedIndex].text = loca3[0]; options[selectedIndex].value = loca3[0];
}}
-->
</script>
<body onload="init()">
<font color=#000000><b>来自:</b><br>请输入您所在国家的具体地方。此项可选<br><br>
省份 <select name="province" onChange = "select()"></select> 城市 <select name="city" onChange = "select()"></select><br>
我在 <input type=text name="newlocation" maxlength=12 size=12 style="font-weight: bold"> 不能超过12个字符(6个汉字)
</form>




三级联动的xml太长了,不粘出来了,可以下载源码