color palette

Hi all-
I am looking to generate a color palette (of a handful of colors) based on a
photo, similar to what kuler <http://kuler.adobe.com/#create/fromanimage> or
some <http://www.degraeve.com/color-palette> other<http://www.colorhunter.com/>
services <http://www.pictaculous.com/> do.  I imagine it is fairly
subjective about how to determine the preferred colors, but any ideas?  I
need a solution that would work and be reasonably fast for large photos with
lots of colors.  I've been reading the quantize
documentation<http://www.imagemagick.org/Usage/quantize/#handling>,
and have been experimenting with the '-posterize' and '-colors' flags -
still haven't nailed it, though.

Thanks!
-Aidan