You can never have too many apps. Check out http://apps.usa.gov/. This site collects apps or mobile sites of US Government agencies. The format varies, some are for iPhone, Android or Blackberry, many are mobile-friendly websites.
Smithsonian, National Library of Medicine, National Center for Telehealth and Technology, Department of Energy, FEMA, FBI, NOAA, and National Weather Service are just a few agencies with apps or mobile sites available.