there are quite a few free brushes out there you can try out. Trouble is, everyone has their own preferences depending on work style, so what works for others may not work for you. Best thing to do IMO, is to try different brushes and see how they work for you. Or better yet: create your very own brushes.
David Levy has an excellent tutorial video here on Gnomon (with brushes as part of the download package) that will help you get a good start, or inspire you to improve your existing brushes.
Hope this helps.