JGraph is the most powerful, lightweight, feature-rich, and thoroughly
documented open-source graph component available for Java. It is accompanied
by JGraphpad, the first free diagram editor for Java that offers XML, Drag and
Drop and much more!

With the JGraph zoomable component, you can display objects and relations
(networks) in any Swing UI. JGraph can also be used on the server-side, for
example to read a GXL graph, apply a custom layout algorithm, and return the
result as a HTML image map.

WWW: http://www.jgraph.com/