I'm not sure if this is a welcomed post but a site which may be of great interest to your group is http://www.projecteuler.net It is a series of mathematics problems, many of which build upon each other, and are generally solved via use of a programming language (such as Common Lisp or J) but are also doable by a "pen and paper" aproach. The problems themselves go from easy to hard a bit quickly but are generally fun to solve and think about. Upon completion of a problem you gain access to a forum which has posts from other users about their own methodologies in the solving of that problem.