Are you using the ASP.NET AJAX controller extenders yet?  If
not, go here, to grab them.  They provide useful functionality
like animating Update Panels, adding Callouts to Validators,
adding Resizing to Controls and much more.  Here's something
even beyond that - a quick video which shows you how to make
your own extenders. Enjoy.  How Do I: Create an ASP.NET AJAX
Extender from Scratch? : The Official Microsoft ASP.NET Site