This map I've done following some amazing tutorials:
[Award Winner] Making Map Borders in GIMP
[Award Winner] Making Photo-realistic Trees in GIMP: A Mini-Tut
and RobA's tutorials:
[Award Winner] Using GIMP to Create an Artistic Regional RPG Map
[Award Winner] Simple Mountains in Gimp
Here is the result:
I am also making a technic (well, I think I am) to make fast and cool looking pseudo-random heightmaps, hope I can make a nice tutorial someday.
Feel free to use this map for any non-commercial pourpose.