I perfer to use a vector program so i use Illustrator but 2nd might be Inkscape.
Free Vector Drawing Programs
Beez --Bezier curve SVG animation. .
CadStd -- Many snaps, polar&rect arrays. Fast and nice.
Cenon -- Give away the program, charge for the books.
Expression -- Will be replaced by Acrylic. Does not expire.
Dia -- Many export options. Primarily for diagrams.
EVE WE -- Tiny (86 KB). Extensive SVG usage on website.
GLIPS Graffiti -- Java/Batik based. Very professional appearance.
Inkscape -- SVG editor. Has intern support from Google.
Ipe -- Editor for simple PDF files. Extensive manual.
jFig -- Java based. Port of XFig. Free for noncommercial work.
jPicEdt -- Java based. Useful for TeX.
JustCad -- Functional, but bare bones.
Karbon14 -- Part of KDE. Formerly Kontour.
LaTeXPiX -- Makes EEPIC or PGF code for LaTeX documents
OpenOffice Draw -- Part of the large O
suite. Excellent.
POTrace -- Raster to Vector convertor. Command Line driven.
PSTricks -- Part of LaTeX. A coding language for diagrams.
Scribus -- Designed for desktop publishing.
Skencil -- Python based. Open Source.
TeXCad -- Very limited. Written in Ada.
TpX -- Tiny, powerful, and easy to use. Python based.
Wintopo -- Raster to Vector convertor.
XFig -- Excellent TeX support.
yEd -- Primarily a graph editor