visualcomplexity.com is an amazing gallery of visualizations of networks. It has collected examples of great network visualizations in many fields of studies. Its goals are more to inspire than to be a manual on how to create visualizations:
VisualComplexity.com intends to be a unified resource space for anyone interested in the visualization of complex networks. The project’s main goal is to leverage a critical understanding of different visualization methods, across a series of disciplines, as diverse as Biology, Social Networks or the World Wide Web. I truly hope this space can inspire, motivate and enlighten any person doing research on this field.