A couple of weeks ago I asked for help with maps and these are the answers I got. All programs run in Windows. They may or may not have other versions.
GIMP A powerful, freeware alternative to Photo Shop, GIMP is considered one of the best graphics programs available. There are a lot of tutorials out there for it as well. GIMP has been around long enough that there are many resources available for it now such as this tutorial on creating space scenes.
Maptools A freeware mapping program that allows you to import pictures and then use them as guides for things like floor plans and outdoor maps. In additions to being able to use objects from CC3 and Fractal Mapper (and others), it has several video tutorials and forums. Even better, once you use it to create maps, you can the use it to run games both in person and online.
Paint.net Similar to GIMP, but not quite as powerful and also free. It’s like MS Paint on steroids. I haven’t tried it but it looks like a good option for newbies. (Pinta is an Ubuntu Paint.net clone.)
Cartographer’s Guild Forums A good place to get feedback and see other maps as well as ask for help.
For more ideas, see this post at the Core Mechanic.
WOOT! I WAS USEFUL! *dances*
[...] Mapping For Beginners [...]