Here are the brushes I commonly use when I do digital work. I made them all myself out by tweaking existing brush presets in Photoshop, and by using real media swatches like watercolor blobs for some nice textured brushes. I use these in Photoshop CC, they should work in previous versions, though. My favorite brush to use is the Stipple 2 brush - it creates a nice, scratchy texture!
I'll update this download periodically as I add brushes and tweak what I've got. Feel free to adjust and edit the brushes as you see fit. Make new brushes out of old ones, share 'em, use 'em, whatever! (Just don't sell them, pretty please!)