GIMP does work on RAW photos. If you have a Mac, you can get a version of the GIMP that has UFRAW (the little chunk of software that makes GIMP play nice with RAW files) packed right in:
http://darwingimp.sourceforge.net .
If you have another operating system, you can get UFRAW as a plug-in at
http://ufraw.sourceforge.net .
I use UFRAW all the time, and I actually have come to like it better than the RAW converter that came with my camera. It seems to have more tools.