Here are some brush sites for gimp/photoshop.
>Gimp 2.6 + (I think :p) can use photoshop brushes as long as they are .abr .

www.outspoken-kate.com
www.rewindd.com
ego-box.com
swimchick.net
artflower.de
www.deviantart.com
thefateof1.com
www.hybrid-genesis.com
celestial-star.net
www.saruna.net
www.at0mica.net

I used some of these but can't remember which site.
;[