If you have a bit of free time on your hands, you can make a calendar in the form of of a regular dodecahedron or a rhombic dodecahedron using the templates created here.
The site generates templates for calendars in 50 languages for any year in either PDF form or PostScript form, which you can later print off and assemble, using the directions provided. I myself made one regular dodecahedron and one rhombic dodecahedron (both in Chinese), which you can see below:
In case you were wondering what a dodecahedron is, it’s a 12-faced solid. In a regular dodecahedron, all edges, vertices, and faces are congruent, with 3 edges per vertex and pentagonal faces. A rhombic dodecahedron has 12 rhombuses as faces, but not all the vertices are congruent (some have 3 edges, others have 4).
Of course the process for making these is a bit different. The regular dodecahedron is made using one sheet of paper with basically the unraveled faces of the solid, which you glue together. The rhombic dodecahedron is made by making 12 parallelogram-shaped pieces which interlock.
A few extra notes on the rhombic dodecahedron: the site says that you need legal size paper to make it. This is not true. You can use letter paper, but you will have to cut off paper around the edges of the starting rectangles. You can figure out how much to cut off based upon the creases made in the folding process. Since the template gives folding guides, you can use those instead of following the steps given by the site and then cut off the parts past the intersection of the diagonal and vertical folds.
Another trick that helps with the rhombic dodecahedron is to tape the back of the 12 parallelograms. This will make them more stable and in turn, the solid will be less likely to fall apart as you make it.
One final note: one of the commenters on the Lifehacker article that led me to this site noted that the blank white of the templates from this site looked boring, so if you agree and want to try to make a more colorful regular dodecahedron, she has a few JPEG templates for 2007 and 2008 calendars (in English) here.