One of my favorite tools when I started using RPG Maker was definitly the
Greenfish Relief Map Generator
x)
This program generates you a random worldmap.
Sounds quite simple and yes, it is.
By clicking on the refresh-button you will get a new random world map, it's also possible to add towns!
It's not really helpful if you already have something really special in mind, but it's quite inspiring if you are just starting your project x)
Greenfish Relief Map Generator is a unique program that enables you to create fake map images that resemble real relief maps, but are completely random. You can customize the map colors, load city names from a text file and also set the map size and amount of water to use.