双向下拉实现需求：

<ul class="ul_demo"> <li>通过左右按钮向右侧列表框添加项或移除项操作。</li> <li>通过双击两边列表框里的项可以进行添加或移除项。</li> <li>获取右侧列表框里的选项值。</li> </ul>

HTML

<div class="select_side"> 
   <p>待选区</p> 
   <select id="selectL" name="selectL" multiple="multiple"> 
      <option value="13800138000">王新安 - 13800138000</option> 
      <option value="13800138001">李密 - 13800138001</option> 
      <option value="13800138002">姜瑜 - 13800138002</option> 
      <option value="13800138002">钱书记 - 13800138004</option> 
   </select> 
</div> 
<div class="select_opt"> 
   <p id="toright" title="添加">></p> 
   <p id="toleft" title="移除"><</p> 
</div> 
<div class="select_side"> 
   <p>已选区</p> 
   <select id="selectR" name="selectR" multiple="multiple"> 
   </select> 
</div> 
<div class="sub_btn"><input type="button" id="sub" value="getValue" /></div>

jQuery

$(function() {
    var leftSel = $("#selectL");
    var rightSel = $("#selectR");
    $("#toright").bind("click",
    function() {
        leftSel.find("option:selected").each(function() {
            $(this).remove().appendTo(rightSel);
        });
    });
    $("#toleft").bind("click",
    function() {
        rightSel.find("option:selected").each(function() {
            $(this).remove().appendTo(leftSel);
        });
    });
    leftSel.dblclick(function() {
        $(this).find("option:selected").each(function() {
            $(this).remove().appendTo(rightSel);
        });
    });
    rightSel.dblclick(function() {
        $(this).find("option:selected").each(function() {
            $(this).remove().appendTo(leftSel);
        });
    });
    $("#sub").click(function() {
        var selVal = [];
        rightSel.find("option").each(function() {
            selVal.push(this.value);
        });
        selVals = selVal.join(",");
        //selVals = rightSel.val();
        if (selVals == "") {
            alert("没有选择任何项！");
        } else {
            alert(selVals);
        }
    });
});