This website has a bunch of free brushes! I enjoy downloading free brushes so I can use them on my projects. I wish that I would've have realized how to do this a long time ago! I feel that they add a little character to my pieces when I use them.
There are many different brushes on her and they are categorized as well. I usually download the 'grunge' type brushes. It is surprising how many different types of brushes are out there. There is basically a brush for everything!