I recently purchased a license for the Hexographer program and it is pretty darn cool. I have zero artistic talent and I have still been able to create some quick maps that while they aren't exactly cartographic masterpieces, don't look too terrible. While the user interface isn't completely intuitive, I still find it much easier to use than any other mapper that I have tried.
The advantages to Hexographer are many. The basic version is free to use online and the pro version costs less than ten bucks right now for a year's license. The program is also written in Java and so it should run happily on almost any platform. I have successfully used it myself on both PC and Mac machines.
You can use the program to generate maps that are reminiscent of the old D&D 'gazetteer' series of modules, but that's not all. You can also generate maps of cities and even star maps for sci-fi games. If you are particularly adventurous, you can even import your own symbols (at least in the pro version).
Also exciting is that the author is planning to release another program called Dungeonographer that promises to do for dungeon maps what Hexographer has done for overland maps. I can't wait!
Below is an example map that I literally banged out in five minutes.