Steve Alvis wrote us about using Blender to import data fromÂ Graph Calc,Â a free graphing calculator for Windows and Linux which can be used to graph 3d functions.
You are not only limited to Cartesian coordinates, but you can use polar coordinates too. The 3d graphs can export to DXF which are compatible with blender. You just have to remove doubles in the edit mode to make it look right.
Nice tip - thanks Steve!