Gephi

http://oss.infoscience.co.jp/gephi/gephi.org/plugins/graph-streaming/index.html
http://gephi.org/blog/

The purpose of the Graph Streaming API is to build a unified framework for streaming graph objects. Gephi’s data structure and visualization engine has been built with the idea that a graph is not static and might change continuously. By connecting Gephi with external data-sources, we leverage its power to visualize and monitor complex systems or enterprise data in real-time. Moreover, the idea of streaming graph data goes beyond Gephi, and a unified and standardized API could bring interoperability with other available tools for graph and network analysis, as they could start to interoperate with other tools in a distributed and cooperative fashion.

Data Set is available at
http://oss.infoscience.co.jp/gephi/wiki.gephi.org/index.php/Datasets.html