Here's an odd, short tutorial. Several people have commented on my use of 3D in creating some of my maps. While I certainly do use 3D applications and sometimes incorporate their use in my maps. My recent Top Down Tree House map in the Finished Map Forum uses implied 3D through creative texture use and shading, however, everything was done in a vector graphics application. The same techniques can be applied to image editors as well.
I often find myself using photo-textures to create certain terrain types, but changes in shape sometimes doesn't match the photo. This tutorial uses shapes to apply the same texture but rotated to follow a different direction. However, it's an odd, corner case problem that may or may not come up in your designs, so I don't know how useful this tutorial really is - just an explanation of how to imply 3D when you don't have the time to spend using 3D applications, as a quick solution. Really, even using 3D applications presenting accurate texture skinning of 3D objects is a lot more problematic and difficult to accomplish, even with the best tools. So this is the cheaters way to do 3D and skip the problem altogether.