效果图如下：

HTML代码如下：

CSS样式如下：

@charset "utf-8";
/* 简单reset */
body, ul, li {
 margin: 0;
 padding: 0;
}
body {
 font: 14px/24px Microsoft YaHei;
 color: #333;
}
ul { list-style: none; }
a {
 color: #333;
 outline: none;
 text-decoration: none;
}
table {
 border-collapse: collapse;
 border-spacing: 0;
 text-align: left;
}
/* 布局样式，非必须 */
.wrap {
 width: 600px;
 margin: 100px auto 0;
 padding: 20px;
 background-color: #d3f3dd;
}
.wrap table th, .wrap table td { padding: 8px 2px; }
.wrap table th {
 font-weight: normal;
 text-align: right;
}
/* 下拉框样式 必须 */
.select-style ul {
 list-style: none;
 padding: 0;
 margin: 0;
}
.select-style select { display: none; }
.select-style {
 position: relative;
 display: inline-block;
 font-family: Microsoft YaHei;
 color: #666;
 font-size: 14px;
 text-align: left;
 vertical-align: middle;
 z-index: 50;
}
.select-style.focus { z-index: 51; }
.select-style .slt-wrap {
 display: inline-block;
 width: 200px;
 border: solid 1px #d6d6d6;
 vertical-align: middle;
}
.select-style.focus .slt-wrap { border: solid 1px #53a8df; }
.select-style .slt-title {
 position: relative;
 display: block;
 padding: 0 36px 0 5px;
 line-height: 30px;
 height: 30px;
 text-decoration: none;
 background-color: #fff;
 word-break: break-all;
 color: #666;
 overflow: hidden;
}
.select-style .slt-title .slt-text {
 display: inline-block;
 height: 30px;
 *cursor: pointer;
}
.select-style .slt-title i {
 position: absolute;
 right: 0;
 top: 0;
 display: inline-block;
 width: 30px;
 height: 30px;
 background: url(../images/ico-select.png) 0 0 no-repeat;
 *cursor: pointer;
}
.select-style.focus .slt-title i { background-position: 0 -30px; }
.select-style.disabled .slt-title i { 
 background-position: 0 -60px;
 *cursor: default; 
}
.select-style .opn-box {
 display: none;
 position: absolute;
 left: 0;
 top: 31px;
 width: 100%;
}
.select-style.up .opn-box {
 top: auto;
 bottom: 31px;
}
.select-style .opn-box .opn-list {
 position: relative;
 _width: 100%;
 max-height: 130px;
 border: 1px solid #d6d6d6;
 background: #fff;
 overflow-y: auto;
 overflow-x: hidden;
}
.select-style.focus .opn-box .opn-list { border-color: #53a8df; }
.select-style .opn-box .opn-list li {
 display: block;
 _width: 100%;
 padding-left: 5px;
 line-height: 26px;
 height: 26px;
 overflow: hidden;
 white-space: nowrap;
 text-overflow: ellipsis;
 cursor: pointer;
}
.select-style .opn-box .opn-list .selected { background: #d4edfe; }
.select-style .opn-box .opn-list li:hover {
 color: #fff;
 background: #65abda;
}
.select-style .opn-box .opn-list li.disabled {
 color: #cacaca;
 background: #f0f0f0;
 cursor: default;
}
.select-style.disabled .slt-wrap { border: 1px solid #d6d6d6; }
.select-style.disabled .slt-title {
 color: #cacaca;
 background-color: #f0f0f0;
 cursor: default;
}
.select-style.disabled .slt-title .slt-text { *cursor: default; }
/* 下拉框样式 结束 */

Jquery代码如下：

兼容到IE7+（IE6其实也行，只是选项多于5个下面不会出现滚动条）。