Russian popular science resource Elementy with physics and mathematics problem collections and explanations.
Russian study-materials portal offering textbooks and problem collections (login-required, includes Meshchersky problems).
Russian physics site offering problems, puzzles, and educational content for learners.
Database of solutions to Irodov, Chertov–Vorobyov, and Volkenshtein problem books.
Moscow School 57 publishes problem collections and solutions in mathematics and physics.
Teacher-maintained archive of physics problems.
Solutions to problems from physics textbooks.
Large teacher file-sharing site including physics problems.