Cheating isn't frowned upon in the work-world, and we are always looking for case-studies and examples that we can modify and use. Not to mention looking for examples to bolster our business cases, "well so-and-so is blogging!" [Note to Joe and John: cheating IS frowned upon in school!!!]
See "Social Media Case Studies SUPERLIST- 18 Extensive Lists of Organizations Using Social Media." Lists include corporate Twitterers, directory of Fortune 500 blogs, and nominees and award winners in various recognition programs with their case studies.
In addition to Robin's fab list, here are some lists from government.
The Collaboration Project from the National Academies of Public Administration for a terrific set of case studies of social media/collaboration in federal, state and local goverments.
Also, see USA.GOV for a number of directories like:
list of government tweeters on Twitter is available at Twitter Fan Wiki.
Don't see your agency's efforts on these lists? Speak up and tell them you are missing. These resources are updated regularly.