World Map is a free program developed by the Center for Geographic Analysis at Harvard University. World Map is designed to enable creation, visualization, and exploration of geographically referenced information. In other words, you can build some great mapped data visualizations on the service.
Target Map is a service that allows anyone to create mapped displays of data sets. Users of Target Map can import and map their own data sets, use data sets from other users, use data sets found online, or manually input data onto a map.
GeoCommons provides excellent tools for creating and sharing map-based data visualizations. Users can select a from twelve base maps to build upon. After choosing a base map users can select from more than 49,000 public data sets or upload their own data sets. Map creators can add more than one data set to their maps. To complete the visualizations users can specify colors, shades, shapes, and apply numerous filters to determine what is or is not displayed from their chosen data sets. Completed maps can be shared as KML files or embedded into blogs and websites.