• yed Free version of a once commercial framework
• prefuse.org very slick transitions; you will want to use Java 6
• jung great demos, doesn’t look as slick as prefuse but might be more powerful.
• gvf Just the basics, probably dead, too.
• JGraph – commercial, thanks to David@jgraph.com.

There is also a collection of algorithms for graphs: JGraphT It uses JGraph as the default UI library but you can use the algorithms without that.