While JHymn could be considered a controversial piece of software, I think that it is a good idea and I find it very useful.
JHymn removes the Digital Rights Management (DRM) included on all songs purchased from the iTunes Music Store. The original m4p file can be changed to a DRM-free m4a file or an mp3.
This app requires a bit of configuring — for example, you do have to specify which unwanted atoms should be removed. (Read the download page for directions.)
While the author of this program does not condone music piracy, nor do I, I do feel OK about stripping the DRM from music that I legally own.