http://www.cut-the-knot.com/content.html

These pages may not help those who are foolishly afraid of mathematics, but the
puzzles should be interesting to anyone who wants to understand more than the
surface of things.

http://www.math.yorku.ca/Who/Faculty/Ganong

Rick Ganong can be hard to take, but he is very generous about sharing ideas,
especially regarding math and logic.

http://www.cs.cornell.edu/home/gries/gries.html

http://webster.cs.uga.edu/~gries/

David Gries is a noted computer scientist and mathematician. Mr. Gries has
strong opinions about the use of logical principles in problem-solving and
computer programming. The second link contains an interesting interactive java
training exercise.

http://www.randomhouse.com/special/puzzles/smullyan/smullyan.html

Raymond Smullyan is a mathematician with a very healthy penchant for puzzles.

http://www.midaslink.com/east/mathmagic.htm

The midaslink site has a Knight's tour game that can be very addictive.

http://tomkonieczko.com/

Tom's art is expressive in an unusual way.

http://www.cs.odu.edu/~toida/nerzic/content/web_course.html

Mr. Toida's interactive exercises in fundamental logic are very well done and
express the fundamental concepts of logic in an elegant way.

The retro site combines
chess and puzzles in a clever way.