NodeXL: Network Overview, Discovery and Exploration for Excel
NodeXL is a free, open-source template for Microsoft® Excel® 2007, 2010 and 2013 that makes it easy to explore network graphs. With NodeXL, you can enter a network edge list in a worksheet, click a button and see your graph, all in the familiar environment of the Excel window.
Website: http://nodexl.codeplex.com.