A Twitter stream of all the federal government agencies various Tweets is compiled here, on what NextGov.com is calling "The Feed." Some examples of the agencies Tweeting include the US Dept. of Labor, the US Coast Guard, and the White House. From the release:
Visitors to The Feed can opt to see all federal tweets in one place or they can select to see only certain categories of tweets, including business and finance, defense and diplomacy, law enforcement, government at work, and the White House.