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.
MathType - The Professional version of Equation Editor- MathType is a powerful interactive tool for Windows and Macintosh that lets you create mathematical notation for word processing, web pages, desktop publishing, presentations, and for TeX, LaTeX, and Math…
PGF and TikZ - PGF/TikZ is a tandem of languages for producing vector graphics from a geometric/algebraic...
KLatexFormula - KLatexFormula is an easy-to-use graphical application for generating images (that you can drag and...
LaTeXDraw - LaTeXDraw is a graphical drawing editor for LaTeX.
Math Magic - MathMagic Equation Editor for Desktop Publishing software & Word Processors, Adobe InDesign, QuarkXPress, MS Word, iWork, for Technical writing with very easy interface and fast input.