Deutsches Reichsgesetzblatt: Researchers might find it helpful to look at issues of the Reichsgesetzblatt (German Law Gazette) for the relevant time period. Here it is, in searchable PDF, made available through the ALEX Historische Rechts- und Gesetzestexte Online of the Austrian National Library.

Encyklopedia Gdańska (Gedanopedia): Beta version of a digital encyclopedia of Gdańsk history, including the Free City of Danzig. Polish only.

Fotopolska: contains almost 7,500 photos of Gdańsk, organized by year or keyword.

Muzeum Strefa Historyczna Wolne Miasto Gdańsk  (Free City of Gdańsk Museum): city museum dedicated to the history of the Free City. Polish only.

Photos of the Free City from MojGdansk.com.