Someone asked about doing cliffs so I put my hand to it.
This tutorial uses Photoshop CS3 and a little bit of Pressure Sensitive stylus but mouse can be used, just be sure to change brush size and opacity often to create a drawn/painted "look" if that is what you are going for.
1. put a layer of black under your map -I did this tutorial with a finished/flattened piece from my Voradin map, so cliffs can be an after the last minute addition to your map.
2. Using the polygonal lasso tool I cut the map layer in half with a jagged edge and seperated the top half to a new layer above the bottom half and the black layer at the very bottom. Next I did a Warp under edit>transform, and just lifted up the lower middle control vertices a bit to actually create a gap between the top and bottom halfs of the map. I didn't touch any other vertices besides the middle ones so the edges on the sides are still in their original positions, creating a tapered mouth-like shape.
3. On a new layer in between the bottom of the map and the black layer I painted in ground with a small hard brush, sampling colors from the map ground areas and drawing in vertical sweeps...I alternated shades and just made it vertically streaky. Then I added noise and faded the noise to about 20%. Then I rendered fibers and faded that to about 20% as well...this roughed it up. I painted way beyond the borders of the actual cliff hole, since the top and bottom map layers effectively mask this area and if I wanted to cut in more details to the top or bottom map layers there would be cliff ground there to expose.
4. As a last pass I used a small hard eraser to rough up the edges of both the top and bottom halfs of the map. Added rocks and debris to the bottom map layer up against the edge of the cliff using sampled ground colors and a small hard brush - I am drawing lighting in here, keeping the top left edges of the rocks brighter and shadowing the right edges, also added shadowing under the top edge of the cliff and in broader stroks to change the shade as the whole cliff face changes angles.