Several of our DC newspapers and reporters are firing out tweets (but they’re not all on the GraphicDesignr’s list):

Washington Times
Politico
The Hill
Washingtonian
FishbowlDC
NPR News
Houston Chronicle’s Julie Mason
CQ’s Eric Pfeiffer

The Washington Post has 13 Twitter pages. Here are a few:
The Fix
The Sleuth
Washington Post Politics

NYC Tweets:
Wall Street Journal
WSJ’s OpinionJournal
New York Times
NY Times Politics

FamousDC’s Twitter page

Hat Tip Katie Harbath