Ole Miss Problem of the Week Contests
The Problem of the Week Contests, containing 5 unique mathematical problems to solve, are designed for children and adults of all ages. Each week thousands of participants from around the globe attempt the mathematical challenges with a Casio calculator being rewarded to one randomly chosen correct problem-solver for each contest.
www.olemiss.edu/mathed/contest/   reviews

Bradley University - Problem of the Week
A new mathematical problem of the week, and a collection of past problems.
bradley.bradley.edu/~delgado/potw/potw.html   reviews

Problem of the Week - When Did Santa Leave
Mathematical problem of the current week, and a collection of problems from prior weeks.
www.math.wayne.edu/~boehm/Probweek.htm   reviews