You might want to try Lineform from Freeverse:
http://www.freeverse.com/lineform/
Got a 2006 Apple Design Award.
Realistically it should be called "Paintform" -- OG leaves it in the dust when it comes to lines, but take a look at some of the user submissions and it does a nice job for drawing and illustrating.
http://www.freeverse.com/lineform/lineform_goods.php