Google Closure Tools. Used by many of Google's services (e.g. gmail, maps, docs, sites, books, reader, blogger, picasa) Heavy weight. It even supports drag'n'drop. At Source code.google.com.
Google OpenSocial API @ Source code.google.com. A API for building social networking sites, so that all social networking sites can have one unified API.
Google Web Toolkit. You use Java to create a GUI app, then the kit will compile it into HTML and Javascript so it can be deployed on the web. Seems that Gmail and GoogleMap is written this way.
Web Devout By David Hammond. @ Source www.webdevout.net [A large site on CSS conformance across browsers, and other articles. Heavily biased against Microsoft.]