Hey guys, i found this nice program on http://www.nbos.com, is called "Fractal Mapper". It seems to be very powerfull, just check out this maps:
General view:
A zoom to a map:
Big city:
Island:
It seems to work as an 'autocad' with the vectors and layers and all that designing stuff. You can download the trial, but you can't save your maps . You can have some fun experimenting until getin' the complete version.