Choose a subject, any subject. Andy Kirk has published a great directory of sites and services for accessing (mostly) structured data sets at his site, Visualizing Data. It’s nicely organized into these categories:
- Goverment and NGO’s (examples include The World Bank and UNICEF)
- Local Data (i.e. city data from NYC and Paris)
- Commercial Services and Marketplaces (an example is Infochimps)
- Social Data (including applications for archiving Tweet data
- Portals and Platforms (other collections of structured data, like Freebase)
- There are also links to Data-Related Movements like the Open Data Institute and Data Search Tools (Get the Data)
I can not wait to start exploring!