Since installing Gimp I have been playing with brushes. After a bit of searching I have found some brushes created by other gimp users which are worth getting.  I highly recommend taking a look at the brushes from Hawksmont, Gimp-tutorials and Various Brushes.  They are of a high quality and a really nice design.

Here is just one example of the hearts brushes available from Hawksmont.

Hawksmont Brushes
 Transportation part 1
Grunge Brushes
Splatters
Fingerprints
Skylines
Fractals part 1
Fractals part 2
Floral part 1
Floral part 2
Guns
Stars
Hearts
Shells
Doodles part 1
Doodles part 2
Dill
Leaves mega pack
Bubbles

Gimp-tutorials.net brushes
Vector Grunge Brushes
Galactic
Grunge Brushes
Arrogance Grunge 2
Odysee Brushes
Fusion Brushes
Grass Brushes
Lithium Brushes
Animated Crayon
Edge Brushes
Feather Brushes
Cubes Brushes
Grunge Ink splats
Floaral Brushes
9 Cool Splatter Brushes

PStoGimp Brushes
Various Brushes including a Harry Potter brush.

Click this linkto see a search for Gimp Brushes on Deviantart. Even though the search specifies Gimp brushes the search results include some Photoshop brushes, so check before you download any.

And finally, these next two links are for brushes which are simple shapes and lines in monochrome (black and white).
1100 Brushes
pgd design, Various brushes

 Please note: It is important to double check the terms and conditions each author has put on the brushes they have created before downloading.  Most of them can be used for commercial and non-commercial designs.  Remember, always check.