The Government Documents Roundtable (GODORT) of the American Library Association has created a Subject Focused Lists of Government Databases site to go along with their 50 State Agency Databases site. It links to lists created by others, such as universities. So far, the only subjects are business (US State Corporations), history (biographical media, newspaper, museum, and official records), and prisoner locater tools. Let’s hope it grows.
Subject lists: http://wikis.ala.org/godort/index.php/Subject_focused
State agencies: http://wikis.ala.org/godort/index.php/State_Agency_Databases