There are a ton of math sites and math puzzle sites. Search for math puzzles, math teasers, brainteasers, and such. Some of these may have changed since last year. I'll update them as soon as I can. They have daily and archived puzzles in a variety of difficulty levels.
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. This is a different kind of site.