Normal mapping is a technique which allows game developers to put in high resolution details on a low poly model. This technique has been around for a while. There are various other algorithms like parallax mapping, bump mapping etc, which typically do almost the same thing. I found this wiki page very useful http://en.wikipedia.org/wiki/Normal_mapping . I was specifically impressed with the external links section which points to various tools and methods in which normal maps can be created. I tried creating normal maps using blender. It was a very good experience. I think it would be helpful if you are trying to implement shaders for normal mapping.
Some Random Stuff i work on.. apart from my job.