Okay, okay, I know already gushed about Dan Meyer and his math tasks only two days ago. But I did the teacher version (aka "quick version") of his Bubble Wrap dilemma at a meeting this week and thought it was great. There are so many areas of math in which you could delve deeply with this problem. I think technically it's aligned with 6th grade, but it easily fit 4th grade's Area & Perimeter standards too. Check it out, and have a good laugh at some of the faces he makes in the video!