The JUNG Layouts
This applet animates the transitions between a series of different layout algorithms with the same renderers:
KKLayout - The Kamada-Kawai algorithm for node layout
FRLayout - The Fruchterman-Rheingold algorithm
SpringLayout - A simple force-directed spring-embedder
ISOMLayout - Meyer's "Self-Organizing Map" layout.
CircleLayout - A simple layout places vertices randomly on a circle