..
...
CheckBox ckb = null;
for (int i = 0; i < dt.Rows.Count; i++)
   {
     //注意不是HTML的checkbox
   ckb = new CheckBox();
   ckb.ID = string.Format("chk{0}", i.ToString());
   ckb.Text = string.Format(dt.Rows[i][2].ToString(), i);//JS要获取它的值
   ckb.CheckedChanged += new EventHandler(ckb_CheckedChanged);
   //ckb.Location = new Point(0, i * 20);
   ckb.Checked = false;
   Page.Form.Controls.Add(ckb);
   }
//js代码如下
function aa() {
   var objs = document.getElementsByTagName("input"); //拼凑的字符串
   var str = ''; //遍历
   for (var i = 0; i < objs.length; i++) {//遍历所有的，被选中的复选框
   if (objs[i].type.toLowerCase() == "checkbox" && objs[i].checked)
   //连接客串
   //str = str + objs[i].nextSibling.nodeValue + ',';//这样取到的是null
    str = str + objs[i].value + ',';//这样取到的是on
   }
   window.returnValue = str;
   window.close();
}

  function aa() {
   var objs = document.getElementsByTagName("input"); //拼凑的字符串
   var str = ''; //遍历
   for (var i = 0; i < objs.length; i++) {//遍历所有的，被选中的复选框
   if (objs[i].type.toLowerCase() == "checkbox" && objs[i].checked)
   //连接客串
     var label = document.getElementById(objs[i].id).nextSibling;
     str = str + label.innerHTML + ',';
    }
   window.returnValue = str;
   window.close();
}