A couple of weeks ago, BjÃ¸rn Sandvik pushed out his thematic mapping engine: http://thematicmapping.org/engine/. It's a nice and simple tool for classifying and visualizing the freely available United Nations OneStop Data.
Unlike most other theming engines, it also handles time very well. I generated a time-history thematic map of internet users around the world and temporally visualized in GoogleEarth:
BjÃ¸rn is continuing to tweak the engine and is in discussions on the OSGeo mailing lists about the appropriate open-source license under which to release the engine.
It's great to see some really compelling next-generation web-based and usable geospatial tools emerging.