Founded five years ago, before data startups were fashionable, DataMarket is concentrating more on selling its enterprise platform these days than on its initial mission as a public data service. However, there are still plenty of data to explore and visualize at the site --listed by country, industry and topic.
While there may not be as many useful data sets here as at other sources, the tools offer some compelling options. For example, in addition to slicing the data and changing visualization types, you can search for events and then add markers to your charts and graphs. You can also add additional data sets after creating an initial visualization.
Note: Not all data sets are free.
Where to find it: DataMarket.com.