Made these brush shapes in Inkscape and turned them into Gimp brush files. There are 28 brushes in all. Have fun!
(Note: The Gimp logo icon is from the Tango Icon set - [link]
(Another Note: The license below for the brush files themselves says you need to attribute me for their usage. You don't need to. Have fun - just make sure you share!
Want to learn how these brushes were created using Inkscape and the Gimp? Check out this tutorial I wrote: The Open Palette: Creating Grungy Gimp Brushes Using Inkscape