I have recently been introduced to a new beta service called FlipTrack.  The service lets you put pictures or slides in a picture format to music that FlipTrack provides for you.

They use a proprietary music file format that enables your pictures to be matched up to transitions in the music.

There are two reasons for this

1. FlipTrack has licensed the music that they provide so the end result is something that does not infringe on copyrights.
2. The file format is specific for the user friendly slide show configuration.

So you could not use say a song from your MP3 or iTunes collection.  As slide show programs go this service works pretty easily.  It is in beta so it will be interesting to see how the service grows.  I suspect that it won't take off too much until people can load up their own music and have it verified for ownership rights and then converted to the proprietary format.

Howeve, if they happen to have the song you are looking for in their library it can be rather interesting.