NATO's digital archive, containing thousands of declassified or unclassified NATO memorandum, analytical reports, and other types of documents regarding the Soviet Union.
Integrated digital archival information system of Poland, containing digital copies of materials from various Polish archives. You can find many materials related to the Soviet Union and Polish-Soviet relations on this site.
Digital catalog of the National Archives of the United States. Here you can find open-access records from different US governmental agencies on Soviet issues.
Integrated digital archive of Hungary's major archives. Here you can find digital copies or digital transcriptions of many Communist-era documents related to Soviet-Hungarian relations.