There are a few scripts (and plug-ins). I'll get you started on one, for now:
http://registry.gimp.org/node/59Use version
shape-path-0.91.scm NOT version shape-path-0.7.scm
I am not aware of your level of understanding for scripts based on geometry, so I don't want to start shooting off a bunch of information. If you need to know more about how to use this script, and others that get posted, just ask.
This script provides the more common of geometric shapes used (stars, pentagons, gears, flowers, spikes, polygons, etc.)
_________________
"In order to attain the impossible, one must attempt the absurd."
~ Miguel de Cervantes