自己手写了个图片自适应切换，功能上很简单，大家也能看到，很明显，代码非常冗余.

<script type="text/javascript">
var imgSrcList="http://www.cnblogs.com/images/cnblogs_com/tobin/144465/r_1.jpg,http://www.cnblogs.com/images/cnblogs_com/tobin/144465/r_2.jpg,http://www.cnblogs.com/images/cnblogs_com/tobin/144465/r_3.jpg,http://www.cnblogs.com/images/cnblogs_com/tobin/144465/r_4.jpg,http://www.cnblogs.com/images/cnblogs_com/tobin/144465/r_5.jpg";
var titleList="美女1,美女2,美女3,美女4,美女5";
var urlList="tobin.cnblogs.com/1,tobin.cnblogs.com/2,tobin.cnblogs.com/3,tobin.cnblogs.com/4,tobin.cnblogs.com/5";
var imgArray=imgSrcList.split(",");//转换成数组
var titleArray=titleList.split(",");//转换成数组
var urlArray=urlList.split(",");//转换成数组
var mainWidth,mainHeight;
var intervalTimer;
var picIndex=-1;
window.onload=function()
{
//获取外框div的宽高
mainWidth= document.getElementById("PicShowMain").offsetWidth;
mainHeight=document.getElementById("PicShowMain").offsetHeight;
document.getElementById("PicMain").src=imgArray[picIndex+1];
//调整图片大小
ChangePicSize();
document.getElementById("PicShowText").href=urlArray[picIndex+1];
document.getElementById("PicShowText").title=document.getElementById("PicShowText").innerHTML=titleArray[picIndex+1];
picIndex=0;
//每隔6秒切换一次
intervalTimer=setInterval(ChangePic,6000);
}
function ChangePic()
{
picIndex++;
//设置滤镜使图片有效果，IE支持
document.getElementById("PicMain").filters.item(0).transition=Math.floor(Math.random()*23);
document.getElementById("PicMain").filters.item(0).Apply();
document.getElementById("PicMain").src=imgArray[picIndex];
ChangePicSize();
document.getElementById("PicShowText").href=urlArray[picIndex];
document.getElementById("PicShowText").title=document.getElementById("PicShowText").innerHTML=titleArray[picIndex];
document.getElementById("PicMain").filters.item(0).Play();
if(picIndex>=imgArray.length-1)
picIndex=-1;
}
function GetPicSize(picUrl)
{
//创建一个image对象,获取图片实际的宽高，放到数组中返回
var size=new Array();
var img=new Image();
img.src=picUrl;
size[0]=parseInt(img.width);
size[1]=parseInt(img.height);
return size;
}
//根据图片实际大小和外框大小，调整img标签的大小,使图片放大/缩小但不变形
function ChangePicSize()
{
var picsize=GetPicSize(document.getElementById("PicMain").src);
if(mainWidth<=picsize[0]&&mainHeight>=picsize[1])
{
document.getElementById("PicMain").width=mainWidth;
document.getElementById("PicMain").removeAttribute("height");
}
else if(mainWidth>=picsize[0]&&mainHeight<=picsize[1])
{
document.getElementById("PicMain").height=mainHeight;
document.getElementById("PicMain").removeAttribute("width");
}
else if(mainWidth<=picsize[0]&&mainHeight<=picsize[1])
{
if(picsize[0]/mainWidth
<picsize[1]/mainHeight)
{
document.getElementById("PicMain").height=mainHeight;
document.getElementById("PicMain").removeAttribute("width");
}
else
{
document.getElementById("PicMain").width=mainWidth;
document.getElementById("PicMain").removeAttribute("height");
}
}
else if(mainWidth>=picsize[0]&&mainHeight>=picsize[1])
{
if(mainWidth/picsize[0]<mainHeight/picsize[1])
{
document.getElementById("PicMain").width=mainWidth;
document.getElementById("PicMain").removeAttribute("height");
}
else
{
document.getElementById("PicMain").height=mainHeight;
document.getElementById("PicMain").removeAttribute("width");
}
}
}
//鼠标移动到图片停止切换
function mmin()
{
clearInterval(intervalTimer);
}
//鼠标移开图片继续切换
function mmout()
{
intervalTimer=setInterval(ChangePic,6000);
}
</script>
<div style="width: 400px;">
<div id="PicShowMain" style="overflow: hidden; width: 400px; height: 300px; text-align: center;"><img id="PicMain" onmouseover="mmin()" onmouseout="mmout()" alt="" src="http://www.cnblogs.com/images/cnblogs_com/tobin/144465/r_1.jpg" style="filter: revealTrans(duration=3,transition=100)" border="0" /></div>
<div><a id="PicShowText" href="http://www.cnblogs.com/tobin/admin/EditPosts.aspx?opt=1#"></a></div>
</div>

代码很简单，没什么特别的地方：

准备写成这种形式:

<script type="text/javascript">
var PicEngine=function()
{
//.
this.ChangePic=function()
{
//.
}
this.GetPicSize=function()
{
//.
}
this.ChangePicSize=function()
{
//.
}
}
</script>

但实在是个人对这个this的用法确实不了解。希望有高手能帮我封装一下。
这个只是最简单的，等我学会了这种方式的初始化以后会写成asp.net 控件,原来封装了一个flash+js实现的，可惜flash不是俺写的，链接不好控制，所以准备自己动手写一个。