I have set up a few simple battleground maps for use with MapTool. I used to simply draw a rectangle the size of my desired map but I think that having these templates is a little faster. I started by making a 1200x1200 pixel image in Gimp and playing with brushes until I had a texture that looked like a field of grass and dirt. Then I reduced it to 600x600 pixels. The default scale for MapTool is 50 pixels = 1 square. If I assume that each square has 1 inch sides, then I have a 1' square tile. Finally, I used the "make seamless" filter so that I could use it to build larger maps. Here is a reduced version of the seamless tile:
From that, I built several images for maps of sizes 2'x2', 3'x3', 4'x4', 4'x3' and 6'x4'. Here is an example of use of the 3'x3' map (the tokens were created using Slick's Minis figures so I cannot share them.)
The pack of maps can be downloaded here or on the Downloads section of my blog.