Make the Cutest Little Boxes.
A top-secret gift project at our house required a paper cone, and I can never remember how to cut one out of a flat sheet of paper. On the Internet I found not only a cone template, but templates for all sorts of geometric solids. If your kids have been dying to make their own dodecahedrons, this is their lucky day. I also found templates for take-out boxes, pie-slice boxes, and other interesting shapes. You know me - I can never resist a good spatial relations project. Here are some links:
Geometric Solids: http://www.enchantedlearning.com/math/geometry/solids/
Odd-shaped gift boxes: http://www.paperzone.com/cornerboxes.htm
More gift boxes: http://www.paperandmore.com/articles/box_templates/
And the cone? It's just a circle with a slit cut from the outside to the center. To make the cone more narrow, cut out pie-slices until the cone looks right when you pull the two corners together. I got an ice-cream cone proportion by cutting out ¾ of the circle. See this rocket project for an example: