AutoRealm, from Andy Gryc Software, aims to meet every GM's mapping needs. Well, it doesn't quite do that, but it comes rather close!
From looking at the available packaged icons, you can tell that AutoRealm was designed mainly for creating fantasy maps, though it could be used to create maps for other setting with some creativity. For instance, I was able to create a map of this western town:
A variety of tools are available to users for mapmaking. One is the aforementioned icons. Granted, there isn't a lot of variety, but there are enough terrain icons to get the job done, and the icons for buildings and markers can be sufficient, given some mojo, can be used for almost any setting. You may have to do some labeling with the text feature, but as long as the map features aren't packed together too tightly it should be no problem. There's also an option for resizing icons, which can come in handy.
There are also the line tools. If you're familiar with Ray Dream, you should be familiar with the method of making fractal lines. You can create filled shapes using the line tools. All you have to do is right-click while drawing after making at least one line. You then select a color to fill the shape. There's also a Scalpel tool for cutting points out of fractal lines. That can be handy if you suddenly decide that you don't need a particular point there anymore.
However, there are a few gripes I have about the software. First, now that it's a download without an instruction manual (unlike the version I received), the learning curve may be a bit steep for some people. Granted, it's nowhere near as steep as something like Photoshop or Dreamweaver, but it'll take a lot of puttering around with the software to figure it out.
Second, there could be more icons. There's been enough fantasy mapping software (though, granted, most of it I've seen has sucked-*coughcough*Campaign Cartographer*coughcough*), but we could do with more icons for more modern structures. With the popularity of Deadlands, western icons could be a strong addition, as could icons for skyscrapers and other sorts of urban buildings (after all, White Wolf games are a very strong market force). There are generic markers for large, nation-scale maps (the star in a circle to denote a capital and so forth).
Third, and your results may vary, but AutoRealm seems to be a bit of a memory hog. I once noticed a 15% drop in available system resources when opening it! Of course, as I said, this may be specific to my machine, which can be a bit bitchy at times.
Fourth, and this is somewhat minor and may just be a bug, the bitmaps generated by AutoRealm don't seem to be viewable by other programs, even Paint! Hopefully someday we'll see a version that will fix this, or perhaps save as a JPG- after all, bitmap files are huge!
However, AutoRealm does have a good help file, so you should be able to figure things out. Also, it's free, and open source to boot! Maybe with some other people working on it, the major problems (specifically the RAM problem) coouldbe fixed quickly. Mr. Gryc probably has a real job, and hence not much time to work on AutoRealm. Overall, for your money (again, none) this is pretty good software for mapping. It can be downloaded at http://www.iex.net/~gryc . Just look in the Download section!