Open data is great, but it's useless if you don't know what to do with it. Sunlight Labs, a group focused on using technology to support open government, recently released ClearMaps. It's an Actionscript framework for interactive cartographic visualization.
In addition to giving designers and developers more control over presentation the project aims to address some of the common technical challenges faced when building interactive, data driven maps for the web. ClearMaps is designed as a lightweight, flexible set of tools for building complex data visualizations. It is a framework not a plug-and-play component (though it could be a starting point for those wishing to make reusable tools).
It's still in the early stages, but developers will want to check this out I am sure.
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Sunlight Labs releases mapping framework, ClearMaps
Sunlinght Labs are the same people that gave us the OpenGovTracker