You can make the call using
<link rel="stylesheet" href="http://ajax.googleapis.com/ajax/libs/jqueryui/1.8.9/themes/base/jquery-ui.css" type="text/css" media="all" />
<script src="http://ajax.aspnetcdn.com/ajax/jQuery/jquery-1.5.min.js" type="text/javascript"></script>
<script src="http://ajax.googleapis.com/ajax/libs/jqueryui/1.8.9/jquery-ui.min.js" type="text/javascript"></script>
You can also link to other Ui themes by changes the name of the theme. In This case change the name base to any other theme name /base/jquery-ui.css to any other theme.
<link rel="stylesheet" href="http://ajax.googleapis.com/ajax/libs/jqueryui/1.8.9/themes/base/jquery-ui.css" type="text/css" media="all" />
Check out the jQuery UI Blog for a link of all CDN links http://blog.jqueryui.com/
If you’re concerned that the Google CDN ever fails or goes down, you can fall back to a local copy when the CDN is offline (this example is baked into templates like HTML5 Boilerplate):
<script src="https://ajax.googleapis.com/ajax/libs/jquery/1.7.1/jquery.min.js"></script>
<script>
window.jQuery || document.write('<script src="js/libs/jquery-1.7.1.min.js"></script>')
</script>