Publication Quality Mathematics Diagrams

Inkscape does wonders. Nowadays, you can even export directly to tikz code.

You should keep in mind that publication quality diagrams are made by publication quality illustrators, who are paid for by publication quality editorial houses...

This probably should go as a comment, but I dont have enough points:

Similar questions at other Stack Exchange sites:

• physics - What software programs are used to draw physics diagrams, and what are their relative merits?
• stackoverflow.com - Language or package for drawing geometric diagrams

Note that it would seem that the exact image used in the question is featured in an answer on physics.SE.