What software can you use to 'crop' a part of an mp3, for instance to use as a ringtone?

Macsome Audio Editor, Macsome Audio Splitter... Either is OK. Macsome Audio Editor (http://www.macsome.com/audio-editor-mac/index.html) is more powerful. With Macsome AudioEditor, you can quickly cut and trim audio, as well as split files. It works with compressed MP3 and AAC formats to edit without the quality loss caused by other editors. Get perfect quality audio when editing natively in the MP3, AAC formats.