NNDB (via information aesthetics) calls itself an “intelligence aggregator” tracking activities and relationships of over 32,000 notable people, both living and dead. The database includes a wide range of people from government, corporate boards, television, sports teams, and other organizations. NNDB Mapper is an intriguing visualization tool for illustrating relationships between people. You can also see how organizations might be aligned where people within those groups have connections, multiple roles or historical context.
When first looking at it, I found it hard to see interesting patterns merely by browsing, but they provide a nice video which explains their techniques for setting up a good map and pruning out the irrelevant parts. I still find that you need to come to this kind of site with a question you would like to answer. There are stories behind the data.
It would be cool if this site offered APIs so that the data would be accessible from other projects.