Silverlight Graph Visualizer
GRender takes as input a text-file of the nodes and edges in a graph, and then chooses a good onscreen layout via a physics simulation. It supports dragging nodes around so you can get a feel for the simulation dynamics, or “unkink” the layout if needed.
There are two sample graphs available online: The adjacencies of the 50 US states and An influence graph for a burglar alarm. Source code is available at the fluxcapacity blog.