Yahoo UI already hit version 3 release, and node.js-compatible version lurks in betas out there. GWT requires java and does not hot-swap/recompile easily, but is indeed a good option. Actually some companies try to build on top of GWT: SmartGWT and Vaadin. It's quite an experience seeing each of them comparing against the other with an opposite conclusions (see this and this). Both of libraries are dual-licensed. Also there's Intelligent Expert JS framework, which is also dual-licensed, but builds on top of JQuery instead of GWT.
And of course you would not want to miss Comparison of JS Frameworks on Wikipedia. The table on that page just does not fit my screen, which is quite a fact for me. Quite interesting profiling results for selectors of aforementioned frameworks might be generated via SlickSpeed selector test.