Mental gymnastics from Mensa International
Ed Pegg Jr.'s math puzzle site, in the spirit of Martin Gardner's
Sam Loyd Cyclopedia of Puzzles
View or download an online copy of Sam Loyd's famous Cyclopedia of
5000 Puzzles, Tricks, and Conundrums, which is in the public domain
VI Hart's Mathematics Blog
Ms. Hart is an amateur mathematician and musician. Her blog shows
the lighter side of math.