I got these all from this article on Gizmodo if you want to see some of the ones I didn't link to.
It's just metadata. What can you do with that? Kieran Healy, a sociology professor at Duke University, shows what you can do, with just some basic social network analysis. Using metadata from Paul Revere's Ride on the groups that people belonged to, Healy sniffs out Paul Revere as a main target.
This video clearly describes the distribution of wealth in America using a set of transitioning charts. The graphics are good. The explanation is better.
In a follow-up to their map of racist tweets towards Barack Obama, the folks at Floating Sheep took a more rigorous route to get around the challenges of sentiment analysis. Over 150,000 geotagged tweets against races, sexuality, and disabled were manually classified and mapped.
4. A bit more lighthearted - http://flowingdata.com/2013/10/14/pizza-place-geography/
This is the point of the map above, which shows the nearest pizza place within a 10-mile radius across the United States. Nice and clean data courtesy of AggData.