GDSPlus is a free add-on that allows you to specify what extensions the new Desktop Search tool from Google will index. This includes the ability to add new extensions not yet supported by Google. You will be able to search the contents of any file that can be indexed as text. Examples include:
Additionally, adding non-ASCII file extensions such as .wav, .rar, .png, .psd etc. will index just the filenames for search (PDF content is still not searchable, however). You can also remove support for any of the extensions that Google included and you do not want indexed.