Wolfram Research
Wolfram Math World: Recreational Mathematics
Recreational Mathematics contains lots of fun links to Mathematical Art, Number Guessing, Puzzles, Cryptograms, and seven other fun topics. Each area is explored in depth and is appropriate for both students and teachers.
National Council of Teachers of Mathematics
Nctm: Illuminations: Personal Number
Find your personal number using your birthday. It is the month + date + year and month X date X year.