Clouds for Mapping, and some basic starting points to give you ideas.
I took a bunch of cloud pictures that you're welcome to use for textures, etc, which I'll add below, but first, some ideas for jumping off points from this original image:
I ended up having to size it down a little, so it would fit the upload limit for the site... so the results might be slightly different if you copy the filter settings exactly on this original (it's 300ppi, 8x12"), but hopefully not too much, and I'm sure you'll do your own thing. These are just quick ideas, anyway. I used ps, but I think the filters are the same/similar for gimp if you use that instead.
The file names tell you what steps I took to get the individual looks.