NodeXL, the free and open add-in for Excel that supports network overview, discovery and exploration. The code and application can be found at http://www.codeplex.com/nodexl.
NodeXL allows for the import of network data in the form of edge lists, matricies, graphML, UCINet, and Pajek files along with CSV and other workbooks.
NodeXL allows non-programmers to quickly generate useful network statistics and metrics and create visualizations of network graphs. Filtering and display attributes can be used to highlight important structures in the network.
NodeXL supports the exploration of social media with import features that pull data from personal email indexes on the desktop, twitter, flickr, and soon, facebook.
Recent features added to NodeXL include faster metrics calculation, larger data sets, new layouts, scales, axes, and legends.