NRICH Problems Take a Challenge! Art of Problem Solving Popular Games
Games! Cool Maths 4 kids Maths Dictionary for Kids.com/ Money games - thanks to Mary for this link! Order of operations Coding arithmetic operators Without lifting the pencil Seven bridges of Konigsberg Egyptian numbers Mayan numbers The origin of zero The Zero Saga & Confusions with Numbers Worksheets, calculators, puzzles and more 
Patterns ... Primes, Factors and Divisibility Is 1 prime? The Prime Pages The sieve of Eratosthenes Probability Central Create a graph Make your own graphs What are your chances? Geometry activities for primary school Creative Java Puzzles (tangrams, etc.) Magic squares Introduction to tilings Totally tessellated Tessellation tutorials March 14 is Pi Day? Investigating patterns The painted cube Fibonacci Numbers and Nature The golden ratio Prisms and pyramids Discovering Polygons and Polyhedra The number line Curious Math RekenNet - Enjoy mathematics Cancer and mathematics The Puzzling World of Polyhedral Dissections
Other Competitions:
South African Mathematics Olympiad South African International Mathematical Olympiad New Brunswick Math Competition UK Mathematics Challenges Math League Contests Australian Mathematics Competition