If you haven't checked out the September drop of the Atlas Control Toolkit (Soon to be renamed ASP.NET AJAX Control Toolkit), you should.   One of the coolest new features is the AnimationExtender, which lets you declaratively animate controls.  Just a few lines of markup buys you cross-browser scripted animation.  Obviously, great potential for abuse and breaking site accessibility, but used sparingly could add some nice effects to your site.

http://atlas.asp.net/atlastoolkit/