I have always used this one
Code:
<p align="center">
<script language="Javascript">
<!--
// original content taken from Nic's JavaScript Page with permission
// lack of these three lines will result in copyright infringment
// made by: Nic's JavaScript Page - http://www.javascript-page.com
var currentdate = 0;
var core = 0;
function initArray() {
this.length = initArray.arguments.length;
for (var i = 0; i < this.length; i++) {
this[i] = initArray.arguments[i];
}
}
link = new initArray(
"LINK CODE",
"LINK CODE"
);
image = new initArray(
"IMG URL",
"IMG URL"
);
text = new initArray(
"ALT TEXT",
"ALT TEXT"
);
var currentdate = new Date();
var core = currentdate.getSeconds() % image.length;
var ranlink = link[core];
var ranimage = image[core];
var rantext = text[core];
document.write('<a href=\"' +ranlink+ '\" target=\"_blank\"><img src=\"'+ranimage+'\" border="0" alt=\"'+rantext+'\"></a>');
//-->
</SCRIPT>
</p>