Hey all, first post here. Lurking around and absorbing tutorials around here has been a blast, so I figured I'd try and add what I can.
I tried some half-hearted searching, but didn't see this particular nugget mentioned anywhere:
http://al.chemy.org/

It's a free, small, quick n dirty paint app with lots of options for randomizations that can output your sketching results as vector on pages in a PDF. I don't have any proper results to show off, but the scribbler module seemed like an awesome tool for wriggly coastlines, rivers and possibly (with tweaking) city streets. Amongst other things, you can let font files on your computer, specificed libraries of vector shapes or microphone input(!) affect line and shape behaviour.

A couple of videos available on the site.