Torsten Sillke
- A professor presents his extensive collection of puzzles which use counting, arithmetic, algebra and whole numbers.
- http://www.mathematik.uni-bielefeld.de/~sillke/

Erich's Puzzle Palace
- Original games using triangles, numbers, squares, equations.
- http://www.stetson.edu/~efriedma/puzzle.html

The Exhibitionists
- Interactive, practical math puzzles relating to the management of a museum exhibit. Sponsored by the (British) National Museums Liverpool.
- http://www.liverpoolmuseums.org.uk/nof/maths

Nick's Mathematical Puzzles
- A collection of an assortment of problems to try to solve, with hints, and solutions. Includes daily update feed link.
- http://www.qbyte.org/puzzles/