All files can be printed without support. Photos shown were printed on a Replicator 2 and sliced using the standard setting on Makerware.
To generate your own printable equations, download the file 2D Function to STL.zip and unzip into a new folder. The workflow is as follows: Edit the constants in "printable 2D graph.py" to select your equation. The included equations are in "custom equations.py", add your own if you feel up to it. Run "printable 2D graph.py" to generate and OSCAD file. Then open the OSCAD file, compile, and convert to stl.
Note: It will require a basic understanding of python to edit or create new equations. I also apologize for the clunky code. Please feel free to improve it (or rewrite).