Several years ago, I experimented with building SVG files based on a repeating pattern. The basic idea was to take a drawn line pattern and repeat it, creating closed shapes. Each shape's color was varied - tint, shade, or color difference. I ended up building a tool to do this, and used it to create the background image on the Resumation login page:

I recently found Anders Hoff's site and read through his posts on generative art. I particularly like the cursive-like line art he generated (he calls them Sand Creatures) - something about the randomness of the objects is very enticing.