Just had a first stab at making an art package. It's a grassy, leafy, grot based effort and the brush presets are set largish, so you may or may not want to scale them down if that doesn't suit your needs and resave as a new preset.
I will get better at this I promise . . . .
If you really want a good grassy brush go with Someonesane's excellent offering though.
They are Stickers by the way.
You can download from this link at Dropbox (also recommended by Someonesane - what a great chap Gaeton is).
(The above link is to a repackaged version that should hopefully load easier - March 14th 2012)
EDIT- Hopefully this second one is a bit more complete, thanks to Gaeton's (as ever) excellent advice. Some tangled hair, scratty grass, weeds and a few drawn pebbles.