Ringtone Maker is one of dozens of apps on the App Store designed to create ringtones from the music and songs already on your phone. While it is possible to purchase ringtones from the iTunes store, and the limits on certain tracks in terms of DRM make it hard to convert any track to a ringtone, this is a well-crafted app that works quite well for free.
Open Ringtone Maker and you can choose to either review the online collection of ringtones created by the app's users--usually home recordings or indie bands--or to make your own ringtone from your music library. While the app never explicitly says that it won't convert DRM protected tracks to ringtones, there were multiple crashing issues with DRM tracks that didn't occur with non-DRM tracks. The lack of clear instruction here makes the performance issues frustrating, but we had no issues converting internal or copyright-free tracks on our devices. The interface is generally very easy to use and loading a ringtone into your device is even easier.
If you are eager for an app that will allow you to create your own ringtones from songs or music you have recorded or that you have the rights to, Ringtone Maker is a very good app in that way. It has some performance issues that are hard to pinpoint the source of; but for a free app, it provides a good number of tools and a fun online library you can look through for new tracks or even just music ideas.