Graphicxtras
... offers hundreds of brushes for Paint Shop Pro and Photoshop.

Photoshop Brushes
... offers hundreds of free as well as commercial brushes for Adobe Photoshop. The free brushes include topics like Flowers & Fronds, Togs, Circles, Celtic, Nottingham, Edible, Textures, Spaghetti, Pearls and Yorick. The commercial brushes cost $10 to $25 per set.