- Nick's Mathematical Puzzles - A collection of puzzles, with hints, full solutions, and links to related mathematical topics.
- Wu's Riddles - Riddles, puzzles, and technical interview questions, with a forum.
- University 'problem of the week', with extensive archives:
- Macalester College Problem of the Week - from Professor Stan Wagon.
- Purdue University Problem of the Week - from the mathematics department.
- Bradley University Problem of the Week - from Professor Alberto L. Delgado.
- Math Contest - from Columbus State University.

- Mathpuzzle.com - A cornucopia of math puzzles and mathematical recreations.
- Art of Problem Solving - A community for avid students of mathematics, with forums, articles, and other mathematical activities.
- Wisconsin Mathematics, Engineering and Science Talent Search - Archive of problem sets and solutions.
- Project Euler - A collection of mathematical/computer programming problems, ranging from easy to challenging, with a forum thread for each problem.

- Interactive Mathematics Miscellany and Puzzles - A treasure trove of proofs, games and puzzles, and other eye openers.
- Mathematical Association of America: MAA Online - Comprehensive resources, including book reviews, regular columns, and a mathematical history magazine.
- Mathematician Biography Index - Brief biographies for almost every important mathematician in history.
- The Online Encyclopedia of Integer Sequences - Identify an integer sequence, find the general formula, and obtain missing terms.
- Eric Weisstein's World of Mathematics - Comprehensive and interactive mathematical encyclopedia.
- Mathematical Quotations Server - A searchable collection of quotations culled from many sources.
- Mudd Math Fun Facts - An archive of mathematical snippets, arranged by subject, difficulty, and keyword.
- The Mathematical Atlas - A gateway to modern mathematics.
- QuickMath - Automated solutions in algebra, equations, inequalities, calculus, matrices, graphs, and numbers.
- Dario Alpern's Calculators - A variety of number theoretic calculators, equation solvers, and factorization engines.
- Frequently Asked Questions in Mathematics - Covers a wide range of topics, ranging from trivia and the trivial to advanced subjects such as Wiles' recent proof of Fermat's Last Theorem.
- Mathematical discussions - Essays attempting to show how various mathematical ideas arise naturally. Written in the spirit of George Polya.
- MathPages - Reflections on miscellaneous mathematical topics.
- The Most Common Errors in Undergraduate Mathematics - A comprehensive survey, discussing likely causes of errors, and their remedies.
- Math Help - Articles, proofs, puzzles, jokes, and math tutoring services.
- Oxford University Undergraduate Students Lecture Notes and Problem Sheets - A wealth of useful material.
- Reciprocal links - Educational and Puzzle Sites