Opening any webpage in a dialog window (tested with SharePoint 2010).

http://pacsharepoint.com/2010/07/open-list-item-modal-dialog-lightbox.html

Note: I had to add the script using SharePoint Designer 2010 as the web editor kept removing the javascript whenever I clicked on save.

Opening an image with a Lightbox effect.

http://johnliu.net/blog/2011/5/9/sharepoint-2010-simple-lightbox-effect-for-large-images.html

Note: I had to modify John’s script a little to get this to work for me.

<script type=”text/javascript”>
$(document).ready(function () {
$(“img.ms-rteImage-LightBox”).click(function(){
SP.UI.ModalDialog.showModalDialog({
url: $(this).attr(“src”),
title: $(this).attr(“alt”)
});
});
});
</script>