Create Your Own Unit of Measurement [mental_floss Blog] - I've heard of teachers taking a similar idea and using it to teach conversion rates, unit rate, proportions, and basically any math topic based in measurement.
Math Food [mental_floss Blog] - From the same blog is a series of examples of food used to demonstrate some really interesting high-level mathematics. You could have the kids make a recipe representing an idea you've been studying recently, or make something yourself as a nerdy reward for your classes.
Scavenger Hunt [via Differentiation Daily] - The ways to remix this one are endless... I like the idea of sending kids on a scavenger hunt that forces them to roam all over the school building (after notifying the appropriate administrators and staff, of course) looking for examples of concepts, taking measurements, solving problems. I never did flesh out my building-wide geometry scavenger hunt idea, but feel free to steal the concept and run with it (but please share if you do)!
Skype in the Classroom: Using Skype to Bring Education to Life [The Innovative Educator] - This one should be a no-brainer: your students and a classroom across the world take turns teaching each other mini-lessons. The cultural and language challenges expand the scope of the lesson, force both sets of students to creatively teach concepts, and almost certainly engage even your hardest-to-reach students. Read more about Skype's program from GOOD.
Why Schools Should Embrace the Maker Movement [GOOD] - I think Make is one of those magazines that should be standard in every classroom library (math or otherwise). But I digress: your kids should be making things--Lego Mindstorms robots or one of a zillion Altoid tin projects. Like the Skype idea above, this is a naturally engaging interdisciplinary project that will force students to apply math in ways they might never have considered before. What could be better than that?