Two recent studies, with interesting visualizations, take a look at the sociability of the Fortune 100. (h/t Daniel Brenikov for the links)
Disclosure: Many of the more social companies are Ogilvy clients.
The consultancy iStrategy created an infographic to help visualize data on the Fortune 100′s social savvy.
NetProspex has another take with a chart of the top 50 companies on Social Media.