Free GM Resource: NWMap
NWMap is an interesting, if not simple mapping program for windows. "NWMap is a free, powerful, tile-based mapping utility designed to help you plan modules for Neverwinter Nights (and you may find it useful as a general RPG mapper as well). The author, Jason Harris, has released the program into the public doamin. NWMap uses context-sensitive drawing algorithms that make mapping complicated areas fast, easy and fun."
I downloaded the zip file and simply extracted the contents. No install files or loading, quick and easy. Not a lot of features, but it was real easy to make a simple enough map, faster than most every other app/program I have. Unfortunately the help files online are long gone, but there is enough info in the FAQ (I think) to have a go at making your own tiles.