I have become quite fond of using "found items" for coastlines. In my case I used a radar map of Titan's north pole, reversing the shapes of the lakes to become the land. It underwent some heavy processing to get to the final form. Using a variety of methods, starting from the regional maps tutorial and transitioning through various techniques used in the Eriond tutorial I was able to go from this:
And, finally, this:
The great thing about this method is that it can used with all kinds of naturally occurring shapes. Shadows on a wall. Stucco patterns. Puddles of water on concrete. Just snap a picture and start doing some editing on it and the result will likely be a pretty convincing, randomized but not too much so, coastline.
Next up, I'll talk about the pain I went through creating heightmaps in GIMP to be used in Wilbur, and some lessons I learned in the process.