On a business trip a couple of years ago I was flying over the river deltas of the Gulf Coast of Texas, and was stunned by the fascinating patterns of the land below. After that, I came home and found that there are lots of Satellite Pictures of the earth that exhibit similarly intriguing patterns. I downloaded some, and applying artistic filters in Paint Shop and adding colors, have created some pretty artwork.
Satellite picture of a Florida Bay, morphed and colorized:
In this one, you can see the rivers...
An unmodified picture of sandbars in the ocean - beautiful just as it is.
Some of my satellite pictures come from NASA: http://photojournal.jpl.nasa.gov/
Or you can go to Google Images, and search on "aerial" or "satellite":http://images.google.com/images