While i worked with Gimp suddenly i was hungry for Brushes and here are several Links to Brushes for GIMP i found on the Web.
Gimp Brushes on DeviantArt
http://browse.deviantart.com/resources/applications/gimpbrushes/
Set of Bruhes on noupe.com
http://www.noupe.com/tools/1000-free-high-resolution-gimp-brushes.html
24 Brushsets on Gimpbrushes.de
http://www.gimpbrushes.de
2000 free Gimp Brushes
http://stylishwebdesigner.com/2000-free-gimp-brushes-for-designers/
More then enough Brushes on Gimpbrush.com
http://gimpbrush.com/
If you have more Sources for good GIMP brush sets feel free to put them in the comments below.