I find IPE to be a life-savior when it comes to generating physics illustrations which come with their share of math toppings. The editor has nice utilities for latching on to the boundaries, intersection, center etc of geometric figures. The spline tool is the best I have seen anywhere. Layers are handled with grace. LaTeX is rendered instantly. It is very easy to produce a multipage document. What more can one possibly want?
Inkscape - Inkscape is a free, open source professional vector graphics editor for Windows, Mac OS X and Linux.
Blender - Blender is the open source, cross platform suite of tools for 3D creation.
PGF and TikZ - PGF/TikZ is a tandem of languages for producing vector graphics from a geometric/algebraic...
ZBrush - ZBrush is a digital sculpting and painting software solution.
LaTeXDraw - LaTeXDraw is a graphical drawing editor for LaTeX.
Cinema 4D - Cinema 4D is a 3D modeling, animation, motion graphics and rendering application.