Dan Van Dorn compiled an interesting comparison of the features and output of relief shading programs. He presented his work at a workshop of the ICA Comission on Mountain Cartography on Mt. Hood in May 2002.
Table summarizing the characteristics of the analyzed programs (pdf, 90kb).
Detailed comparison (pdf, 1,724kb).
The links on the right point to descriptions of programs used for relief shading. The lists are in no way complete and the presented software is untested. Expensive GIS applications do not receive description.