The SOMToolbox has been released as OpenSource Package. It is written in Java and features a module for SOM training as well as an advanced viewer application, which implements a large range of different visualisations and quality measures of the SOM. These allow in-depth analysis and evaluation of the trained maps and the characteristics of the data, resulting in a powerful tool for data mining.
Details: http://www.ifs.tuwien.ac.at/dm/somtoolbox