Free Puzzle Collections
Educational and recreational puzzles for teachers, students and parents. 1000 puzzles collected, including Geometry, Logic, Math, Misc, Weight and Moves categories. Every puzzle has an image, hint and solution. Be a member for puzzle solutions.
http://www.freepuzzles.com/
MathPuzzle.com
Math Games, Math Puzzles, and Mathematical Recreations
http://www.mathpuzzle.com/
Rocket City Math League
Science, Math, Recreations, Competitions - Rocket City Math League. International mail-in competition for avid students in mathematics.
https://www.rocketcitymath.org/
Great Plains Math League
Science, Math, Recreations, Competitions - Great Plains Math League. Sponsors several high school math contests in Missouri, Iowa and Kansas.
https://mathleague.org/
USA Mathematical Talent Search (USAMTS)
Science, Math, Recreations, Competitions - USA Mathematical Talent Search (USAMTS). A free mathematics competition available to all high school students in the United States.
https://www.usamts.org/
MATHmodels
Science, Math, Recreations, Competitions - MATHmodels. A online team competition where students compete to solve real-life problems using mathematical modeling.
https://www.mathmodels.org/