Matt Berseth has written one brief post describing how you can incorporate the YUI style progress panel into your existing ASP.NET AJAX web application. He calculated the center of the control and manually placing the progress panel over the center of the rendered GridView. He made the calculation using the OnUpdating and OnUpdated animations of the UpdatePanelAnimationExtender. You can view the full tutorial on YUI Style AJAX Progress Indicator.

Requirements: YUI Framework
Demo: http://mattberseth2.com/yui_style_ajax_progress/
License: License Free