TBC by Tin - Just starting to look at this now.
Research
jQuery - Has become the de-facto standard, but I am also looking for a commercial option for web applications.
Sencha - HTML 5 Platform with tools to visually build for mobile and desktop web applications. Buy license.
Vaadin - Open Source integrates with Spring Roo.
Vaadin is GWT based. So I am taking it off the list right away.
YUI - Tried before, the only thing is it is very slow.