A collection of mapping tools recommended by other GMs.
I must highly suggest using the spreadsheet tool from googledocs for beginners. It ain't pretty, but it is easy and fully online. - itsgottabeodin
MapTool. This is what I use for my PbP games. It's primarily of use to iRC games, but it is a snap to lay out a tactical situation, take a screenshot, and slap it into a post here on Myth Weavers. - Chemalle
I have used TTOPRPG for years as a mapper. I find that it uses less system resources then say Maptools. - Hunterindarkness
I use a combination of GIMP and Dundjinni. I have been using Dundjinni for years and have a large supply of user created artwork. GIMP is basically a freeware open source Photoshop, if you know what you are doing. I know enough to be dangerous. the feature I really like is the ability to use layers. I tend to have one layer for the background map, one layer for each character token, a layer for monsters, a layer or two for effects...suck as darkness, mist, or area of effect for spells. - TatteredKing
Might check out Ditzie as well. Run by a member of Myth-weavers, it's a whiteboard mapping too. - drkrough; I've moved to exclusively using ditzie. I highly recommend that as well. - itsgottabeodin
Flip Maps: Even if the Scenario isn't in here, chances are you'll be able to cobble something together from the Flip Maps.
Note: If you can't find the map you're looking for, try the Flip Maps (especially if is marked as such in the scenario).
Once you do that and you're logged in, you can add maps and tokens etc. by clicking "Your Album", again in the top right, then clicking "Add Items", and uploading the jpgs etc. I usually deal with cropping and resizing jpgs in MS Paint because it's really easy.