Thanks to links from Sarah Pendergrass, I stumbled upon this awesome program for graph visualization and analysis called Gephi. It seems rather feature rich, with built in connectors to database systems, extensive graph coloring, layout, and rendering features, and several analysis tools. Gephi is an open-source project.
(http://gephi.org/)
To see an interactive example, check out the Diseaseome (http://diseasome.eu/map.html)