GWT-Ext is a powerful widget library that provides rich widgets like Grid with sort, paging and filtering, Tree’s with Drag & Drop support, highly customizable ComboBoxes, Tab Panels, Menus & Toolbars, Dialogs, Forms and a lot more right out of the box with a powerful and easy to use API. It uses GWT and Ext.
The company description above says it all. Nice set of controls which support Ext 2.0.
Check out some demos here.