Problem of the Week Gold

I saw a question on Twitter earlier tonight asking for good Problem of the Week resources. A light brain-wracking produced four ideas. A search through old bit.ly links revealed a fifth. Here’s what I suggested:

I’ll admit, mixed in there I’ve got two definitely-not-problem-of-the-week resources, and one problem of the month website. But still, they’re all fantastic resources, and go-to places for me when I’m looking for a rich problem.

What are your favorite resources (online or in print) for rich problems that might serve teachers and students well in a POW or POM context? Have a thought? Drop a line in the comments!