Visualization of graph data is incredibly challenging, particularly when it comes to extremely large, scale-free graphs and social networks. A few simple searches on the Web and you will find some mesmerizing and very cool images. Perhaps the most cited...
R. Jäschke, A. Hotho, C. Schmitz, und G. Stumme. Proc. 18. Workshop Grundlagen von Datenbanken, Seite 80-84. Halle-Wittenberg, Martin-Luther-Universität, (Juni 2006)