Google has created an integrated online system that lets you store large amounts of data in spreadsheet-like tables and gives you tools to process and visualize the information. It’s particularly good at turning geographic data into compelling maps, with the ability to upload your own custom KML outlines for areas like political constituencies. There is also a full set of traditional graphing tools, as well as a wide variety of options to perform calculations on your data.
Fusion Tables is a powerful system, but it’s definitely aimed at fairly technical users; the sheer variety of controls can be intimidating at first. If you’re looking for a flexible tool to make sense of large amounts of data, it’s worth making the effort.