Simutrans: Relief maps
Beside the relief maps, generated by Simutrans itself, it is possible to import maps as PPM. The altitude is configured by some 20 greyscales. This allows to convert and import normal maps for Simutrans.
The cards on this site were produced with Gimp, the GNU Image Manipulation Programm, which does a really good job.
A collection of relief maps for Simutrans is available at Simutrans Maps.
This map is huge. Really huge! It requires several GB RAM and a quite actual CPU, otherwise using it will avoid fun. It is based on a smaller map. Some nice-to-have are added, i.E. Hamburg harbour and mouth of Ebro. This map is surely not finished. It will be developed further more or less frequently. Some 4000 by 3500 tiles are presenting a good base to construct complex transportation networks not that far from reality. Another possibility of use is to extract smaller parts of Europe. This card is published under GPL.
Almost the same map, aber scaled to 1280 x 1130 px. This one should be useable on "normal" Computers as well. This map is published under GPL.