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