The Virtuelle Fachbibliothek Osteuropa (ViFaOst) has a special page listing digitised primary sources relating to the history of Eastern Europe:

• 100(0) Schlüsseldokumente zur russischen und sowjetischen Geschichte (1917-1991): Digital sources with comments and bibliography, see also this entry.
• Digitale Bibliothek der keramischen Technologie: Ceramic Technologies Digital Library (CTDL).
• The "Freising Manuscripts": Online facsimile of slavic texts from bishop Abraham's missale.
• Monthly Reports about the Development in Poland: Online edition of the monthly reports published by the Ostbüro of the Social Democratic Party of Germany (SPD) from 1956 until 1965.
• Sibirica: Books, maps and manuscripts from the exploration of Sibiria and the North Pole region.
• Sigismund von Herberstein: Rerum Moscoviticarum Commentarii: Synoptic Edition of the Latin and German editions, Basel 1556 and Vienna 1557.