For a more in-depth review of the best sources for specific countries and topics, consult the Slavic Reference Service's research guides to dozens and dozens of fields of inquiry for countries all over Eurasia. Just a few examples:
Reference Sources on Bulgarian History
National Bibliography of Lithuania
Former Yugoslavia National Bibliography
Guide to Russian Government Publications
Guides to Sources on Russian Military Science
Russian Bibliography of Bibliographies
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Michigan State Law Librarian Barbara H. Bean's "Guide to Transboundary Freshwater Treaties" and its update by Arundhati K. Satkalmi of St. John's University, which leads to an unbelievable number of high-quality websites, including Oregon State University's "Register of International River Basins":
The Eurasian region is famous for its shifting borders, its radical political about-faces, and the geographical name changes that go along with them. Resources like the Russisches geographisches Namenbuch (whose entry for all the villages named "Nikitovka" is reproduced above) and Imena gorodov, vchera i segodnia, 1917-1992 : toponimicheskii slovar' (see its entry for the capital of the Komi Republic in the Russian Federation, below) can help to make sense of seemingly-contradictory information or unexplained lacunae in the documentary record.