If anyone still hasn’t sorted themselves out with a calendar for 2013 – come on people, it’s February! – there’s a nice example of one here. It’s a dodecahedron which, once assembled, you can presumably orient to display the correct month (or the incorrect month, if you’re an impish sort).
The best thing about it for fans of LaTeX (the majestic mathematical markup language of kings) is that this thing is written entirely in LaTeX, using the TikZ package to create the graphics.
Download: PDF and TeX files, as well as all necessary packages, are available from TeXample.net.
(If you can’t compile the calendar yourself and want an up-to-date version, click on the Open in writeLaTeX link).