since I was unhappy with the normalmap generators I tried (like GIMP normalmap plugin or Nvidia Photoshop plugin) I started to write my own several months ago.
It supports normal, spec and displacementmaps, stack processing of multiple images and it is completely multithreaded.
I also implemented some ideas I had to improve normalmap generation, e.g. the “Keep Large Detail” feature to preserve overall surface curvature in high-resolution normal maps. Here’s an example, for example renders see the features page:
Tell me what you think, suggestions, bug reports and feature requests are welcome.