"Epistemic games are computer games that can help players learn to think like engineers, urban planners, journalists, lawyers, and other innovative professionals, giving them the tools they need for a changing world."
What is Project Euler?
"Project Euler is a series of challenging mathematical/computer programming problems that will require more than just mathematical insights to solve."
"Do you own an iPhone? Do you also have toddlers or kids who are about to enter school? Put the iPhone and the kids together with some of the apps listed below to keep the kids busy as they prepare themselves for school."
From the same stable as the marvellous xkcd comic, 'what if' is a blog providing a series of crowd-sourced 'what if' questions ... and answers. A potentially rich source of intriguing questions to set your students the challenge of answering.