I once created a large fantasy 3d-like map with Painter 7 (which is a few years ago - Painter 11 is the current version) so despite its rather high price I think it should be mentioned, too:
http://www.corel.com/servlet/Satelli...3#tabview=tab0

I have not tried ArtRage for a map yet, but this one is similar to Painter but much cheaper. More info can be found here:

http://www.artrage.com/

jester