Inkscape

"Inkscape is a professional vector graphics editor for Windows, Mac OS X and Linux. It's free and open source."
Download at http://inkscape.org/en/.
More info at http://en.wikipedia.org/wiki/Inkscape.

Inkscape: Guide to a Vector Drawing Program

"This book serves as both a textbook and a reference for using Inkscape to produce high-quality drawings. It includes a series of tutorials followed by chapters that cover completely each facet of the Inkscape program. The book is full of tips and notes to enable the user to make the best use of the program."

Inkscape: Guide to a Vector Drawing Program at http://tavmjong.free.fr/INKSCAPE/MANUAL/html/.