Program for drawing simple diagrams
 

I'm a materials researcher and I try to use open source tools like gnuplot etc as often as possible. I often need to draw simple line-art diagrams of things and I was wondering if there was a good program for doing this. I have used Microsoft Paint-type programs in the past but something that is optimized for drawing line-art diagrams and generates vector output would be better, that is, faster and higher quality. Ideas?

you might be interested in one of these

http://www.gle-graphics.org/
http://asymptote.sourceforge.net
http://math.holycross.edu/~ahwang/epix/ePiX.html

they all can output to postscript

Inkscape is for general purpose vector drawing, it could be used depending on the concrete purpose. Dia is specific for diagrams, you could check it as well. Also, koffice has a diagram tracer called kivio.

I am sure that there are many more around.