There are other resources of interest on the Net related to the GIMP. The main starting point is Federico Mena Quintero's page at http://www.nuclecu.unam.mx/~federico/gimp/index.html. Quartic, as he's known to the GIMP world, has links to most other GIMP resources.
Nem W. Schlecht's Tutorials Reference: http://abattoir.cc.ndsu.nodak.edu/~nem/gimp/tuts/. The primary site to go to when searching for a GIMP tutorial.
Zach Beane's GIMP News page: http://xach.dorknet.com/gimp/news/. All the latest in the GIMP world.
The GIMP Plug-In Registry: http://gimp.foebud.org/registry/. Where all Plug-In developers register their plug-ins. You can often find plug-ins that are not in the base distribution here or simply grab the source for the latest version.