Here is my contribution:
The original was my favourite picture from all that I took in 2006:
I used The Gimp. First I took two copies of the image, desaturated one with the built-in command (quick but quite flat) and desaturated the other using the channel mixer. I then merged the two together to get a balance I liked.
Next, I took a copy of the composite monochrome image, blurred it by 10px and set the new layer in overlay mode. Opacity was adjusteded to 40%, which increased the contrast without going over the top. That was all flattened and saved as greyscale to give my final result.
I still prefer the original image, as the colours were very complementary and helped pick out the blobs of lichen, but am also happy with this monochrome version.
Wulf