Houghton Mifflin:  Brain Teasers.  http://www.eduplace.com/math/brain/

Brain Bashers,  http://www.brainbashers.com
    Logic, math, language and paradox puzzles.

Quantum Brain Benders:   http://www.quantumbrainbenders.com
    Math-based puzzles. They have daily and archived puzzles in a variety
     of difficulty levels.

MATHSTORIES: http://www.mathstories.com/

Binary Arts, http://www.webgames.com

Mrs. Glosser's Math Goodies:  http://www.mathgoodies.com
       Mrs. Glosser's Math Goodies is a free educational web site featuring interactive math
       lessons. Lessons use a problem-solving approach and actively engage students in
       the learning process. They also offer a Math Chat Board, Math Puzzles, a Math Image
       Library, Educational Links, Homework Suggestions, and more.

Interactive Mathematics Miscellany and Puzzles:http://www.cut-the-knot.com/
       Math puzzles. Interactive education. Information for teachers, students and parents
 

Fooble:  http://www.flooble.com/perplexus/
 

FUN BRAIN:  http://www.funbrain.com/
 

BRAINGLE"  http://www.braingle.com/Math.html
 

This is a different kind of site.  Have you heard of Car Talk on the radio?
http://cartalk.cars.com/Radio/Puzzler/index.html