EDIT: Updated southern landmass, and started on outlining the mountains in the north. Which I think I'll redo and make them cleaner and more even looking.
While waiting for a large program to finish a test run at the university servers, I sat down and put a bit of work into a Campaign world I've been wanting to do for awhile. I made use of some of the tips RobA has posted around the forums, and learned a fair bit about GIMP and Photoshop I didn't know before. (Like how Photoshop Elements doesn't like my trying to copy paste things from GIMP, good old MS Paint saves the day once again.)
The style I will be working on will hopefully produce more of a hand drawn/coloured look to the finished map, I'm currently debating how best to do the mountain ranges, and I'm looking around for older maps. I think I might just use simple iconic mountains with a slight shadow to them.
The North West will be divided into 2 or 3 kingdoms, the South East will have each small island as a city state, and some of the larger ones split into as many as 4. North East will contain maybe 5, as will the South West. I might expand the ocean boarder to add 'extras', and in all, I planned the scale to have the North West island to have about the same landmass as the UK does in the real world.
Generating the outlines in GIMP worked well. Did a Black and White 'shadow' map of the general regions, and multiplied the Blurred (100pt Gaussian) Shadow layer onto a Render: Solid Cloud. I found that adjusting the Cloud's Color Levels to output around 50=60 on the dark, and also lowering the light side produced slightly better results.
For finer details and control over sections I used layers, building up a small section at a time. Draw a small section the size you want to start with, follow all of RobA's steps till you get to the outline. Hold off on taking the outline, and generate a new set of layers, overlapping the earlier layer slightly for a good line up. Before you set the threshold level, set the current working layer to 50% Opacity lets you have a great view of how your landmass will form compared to the original. After, use the Magic Wand tool and crop all the black out, and merge into the base.
Wash, rinse, repeat till you have your land mass with key bays and islands you wanted, with a lovely randomized coast line.