Javaref.com is a new Ajax-driven Javadoc repository the currently includes packages from 85 projects. Java API documentation is displayed in a style that is radically different from the classic javadoc style that generated with JDK. The documentation includes class source code (where available), ability to leave user notes and ability to transparently navigate between APIs by following code references. Search includes auto-complete and there is a floating DHTML class method browser.
Sun's JDK is not included because it is copyrighted.
Javaref will be incorporating the JDK from Harmony as it gets built. The site itself was built with the Tapestry web framework.
The next release will allow users to upload their own javadocs to the repository.