Ringer.org is a free ringtone maker to make ringtones from any song or audio file.
Browse an audio file or upload from the Internet. Input file formats: AAC FLAC M4A MP3 OGG WAV WMA.
Find the portion of the song you like by moving markers.
Set the ringtone file format and delivery mode. M4R for iPhone, MP3 for most of the others.
Convert the song to a ringtone by clicking Make Ringtone.