Bounce, a set of Java and Swing extensions, including ... layout managers like a FormLayout and CenterLayout, image filters, a comprehensive messaging mechanism, a XMLEditorKit with syntax highlighting and automatic indentation and more.
Download the latest version (0.9) which includes a new Wizard framework, Preferences dialog framework, CardPanel, URIUtils, QDialog, ResizingFlowLayout, RunnableAction, ThreeStateCheckBox, MenuUtilities and a DummyIcon. Please see the XML Hammer project for implementation examples.