I always wondered how those cool fractal brushes are made. So, now I got some free time to google it, I discovered that the secret is a free program called Apophysis. I played a little with it and this is what I came up with: a set of 9 thorny brushes that can be used to create really cool stuff.
The brushes are compatible with Photoshop CS3 and above. Have fun with them, they’re free!