15 Puzzle of Sam Lloyd
   Play online Sam Lloyd's "15" puzzle. The funny story and mathematical implications of this game. Some funny logical problems with the 15 game.
   http://www.holotronix.com/samlloyd15.php

A+ Math
   Interactive math help for K-12 students with flashcards, Math Wordfind, Homework Helper and worksheets.
   http://www.aplusmath.com/

AIMS Puzzle Corner
   Provides over 100 puzzles with the goal of creating an engaging learning environment.
   http://www.aimsedu.org/puzzle/

Aha! Puzzles
   Puzzles, books, games and tests with designed by Lloyd King, author of "Test Your Creative Thinking".
   http://www.ahapuzzles.com

Algebraic Math Puzzles
   A collection of puzzles at high school level. Does not include answers.
   http://www.lifesmith.com/mathpuz1.html

Alien Tiles
   Object of puzzle is to try to get color pieces to create certain patterns in cube.
   http://www.alientiles.com/

Alphametic Puzzles
   Numerous puzzles, links, puzzle solver, and a generator.
   http://www.tkcs-collins.com/truman/alphamet/

Alphametics and Cryptarithms
   Puzzles in which letters or symbols are substituted for the digits in an arithmetical operation like addition.
   http://www.mathematik.uni-bielefeld.de/~sillke/PUZZLES/ALPHAMETIC/

Archive Creative puzzles
   Interactive puzzle archive with descriptions for puzzle construction and a special childrens puzzle page.
   http://www.creativepuzzels.nl

Ben Robinson's Cross-Number Puzzles
   A collection of cross-number puzzles: similar to crosswords, but using digits instead of letters. Many involve complex mathematical reasoning.
   http://www.users.bigpond.com/bendr/xwd/numeric/index.html

Brain Teasers and Maths Puzzles
   Interactive logical and mathematical puzzles with feedback and detailed solutions.
   http://www.syvum.com/teasers/

Calculus-Help Problem of the Week Archive
   Calculus based problems range from easy to difficult.
   http://www.calculus-help.com/problem.html

Colorful Mathematics
   Educational software presents advanced mathematics to K-12 students in a game-oriented approach, using coloring and drawing techniques to illustrate concepts from graph theory and computer science.
   http://www.math.ucalgary.ca/~laf/colorful/colorful.html

Contest Center Cryptarithms
   Examples of cryptarithms, with prize competitions for subscribers.
   http://www.contestcen.com/rithms.htm

Dick's Math Puzzle Page
   A collection of mathematical puzzles, some original, with fully worked solutions.
   http://www.mod2.org/

Downloadable and online games
   A variety of Flash- and Java-based games and puzzles.
   http://www.gameintellect.com/

Free Puzzle Collections
   Educational and recreational puzzles for teachers, students and parents. Each puzzle is graded by difficulty and has a hint. Solutions are available to members.
   http://www.freepuzzles.com/

Group Games
   Animations that develop the theory behind such puzzles as the Rubik cube.
   http://www.dmi.units.it/~logar/duek2/index_engl.html

Interactive Mathematics Miscellany and Puzzles
   Java-based math resource including articles, puzzles and links.
   http://www.cut-the-knot.org/

Logicville
   Educational puzzles, brain teasers, and word games such as anagrams, cryptograms, alphametics, doublets, tangrams.
   http://www.logicville.com/

Magic Math Kingdom
   Learn math through games and quiz-oriented tutorial.
   http://www.nes-lab.com/english2/

Math Puzzles
   Logic puzzles and riddles with some solutions.
   http://www.math.utah.edu/~cherk/puzzles.html

Mathematical Games
   A collection of pencil and paper games with mathematical content. Many can be played through the site.
   http://www.madras.fife.sch.uk/maths/games/

Mathematical Recreations
   Detailed exploration of a selection of mathematical topics.
   http://www.mathrec.org/

Mathproblems.info
   Over one hundred and fifty math problems ranging from basic math to differential equations.
   http://mathproblems.info/

Mathpuzzle.com
   Celebrates math puzzles and mathematical recreations.
   http://www.mathpuzzle.com/

Mathschallenge.net
   A website dedicated to the puzzling world of mathematics, with a discussion forum.
   http://mathschallenge.net/

Mathwizz
   Interactive math problems for abilities ranging from middle school to university.
   http://www.mathwizz.com/

Mixed Up Math
   Logic problems, where equations are mixed up. In various formats like boxes, crosses, diagonals, mazes. Free download.
   http://www.kprobe.com/kprobe/mu.htm

Nandor's Exhaustive Chemical Words Pages
   Lists all the English words, word squares, and magic squares that can be written using chemical symbols.
   http://www.wellington.org/nandor/chemwords/chemwords.htm

Nick's Mathematical Puzzles
   A collection of puzzles, with hints, solutions, and links to related mathematical topics.
   http://www.qbyte.org/puzzles/

Paul Hsieh's Puzzles
   Logical and mathematical brain teasers, with an indication of difficulty. Hints are provided; solutions are available by email.
   http://www.azillionmonkeys.com/qed/puzzles.html

Perfect Times
   Teaches and assesses fluency of multiplication and division tables using online cards. Submit data and compare results.
   http://www.perfect-times.co.uk/

Polyhedra Links
   Pastime and activity links for various geometric patterns, polygons and polyhedra by Jill Britton.
   http://britton.disted.camosun.bc.ca/jbpolyhedra.htm

Polymorf - Symmetry of Polyhedra
   A demonstration of the symmetry and transformational properties of the Platonic and Archimedean solids.
   http://www.polymorf.net/

Problem Solutions
   Archive of problems and solutions, compiled by Dr Alec Mihailovs of Shepherd College.
   http://www.shepherd.edu/mathweb/solutions.html

Puzzle of the Week Archives
   A collection of puzzles, with hints and full solutions. Compiled by George Moody.
   http://ecg.mit.edu/george/puzzles/

Puzzles of Leonid Mochalov
   A variety of challenging geometrical and arithmetical puzzles, many with solutions.
   http://puzzlemochalov.com/

Pythabacus
   Description and instruction of using the ancient Pythagorean Abacus to do arithmetic.
   http://www.pythabacus.com/

SMSU Problem Corner
   Math challenges Southwest Missouri State University in three levels of difficulties.
   http://math.missouristate.edu/~les/POTW.html

Scott Kim
   Puzzles for web, computers, and print; ambigrams.
   http://www.scottkim.com/

Sequence Puzzles and Problems
   With links to related sites. Compiled by Torsten Sillke.
   http://www.mathematik.uni-bielefeld.de/~sillke/SEQUENCES/

Storkey: Two Envelope Paradox
   A tough but simply defined problem which demonstrates key issues in probability.
   http://www.anc.ed.ac.uk/~amos/doubleswap.html

The Contest Center
   Classic puzzles and riddles requiring only simple logic and elementary math.
   http://www.contestcen.com/classic.htm

The Enigmatic World of Philip Carter
   Collection of brain teasers from the author of IQ books.
   http://www.knowl.demon.co.uk/

The Little Math Puzzle
   The Little Math Puzzle has been a K-12 Internet activity since 1995 for grades 5-9. Currently the puzzles have ceased but the site maintains complete archives of past problems.
   http://www.sprucelog.com/lmp/

The Puzzling World of Barry R. Clarke
   Brain teasers, articles and puzzles forum.
   http://barryispuzzled.com/

Torus and Klein Bottle Games
   Collection of Java-based educational puzzles.
   http://www.geometrygames.org/TorusGames/index.html

Wu's Riddles
   A collection of riddles, puzzles, and technical interview questions, with a discussion forum.
   http://www.ocf.berkeley.edu/~wwu/riddles/intro.shtml