WEAVE, the Web-based Analysis and Visualization Environment, allows users to present large data sets in some really interesting ways. The open source tool from the Institute for Visualization and Perception Research and the University of Massachusetts Lowell and the Open Indicators Consortium, allows users to create dashboards of information for exploration and discovery.
Particularly good for academic and professional users, authoring is not difficult (though not that intuitive, either).
Dashboards can be configured with selections from different visualizations and users can interactive with the data in interesting ways.
Check out this implementation of Obesity Rates by State.