Are you looking for FREE grunge
Brusheezy have a massive range of brushes which you can filter to gain access to their hundreds of FREE grunge photoshop brushes.
Bittbox have 5 sets of grunge wings providing 10 brushes in total.
The Outlaw Design Blog have a range of photoshop brushes which are free. Some of the best brushes in this post are on that blog.
We Function have a free grunge brush set holding 33 subtle grunge textures and effects. They have a lot more to offer so head over.