The Shape Paths script (
http://registry.gimp.org/node/59) can create a wide variety of shapes:
Quote:
This is a collection of Script-Fus that create Paths in the form of geometric shapes. Squares, rectangles, rounded rectangles, circles, ellipses, ovals, polygons, stars, flowers, gears, triangle waves, square waves, and sine waves are currently supported.
You can create concentric circles and polygons by creating a series of circles/polygons with a common center and increasing radius.
I frequently use these scripts and they work quite well.
Mahvin has written a very good tutorial for this script:
http://www.mahvin.com/?p=1994