Ringtones for Mac

From The Little App Factory:

Make Ringtones for Your iPhone

Create high-quality ringtones for your iPhone simply and easily. More cost-effective than the iTunes Store, and easier than GarageBand, you can turn any DRM-free song in your iTunes library into a ringtone.

Simple and Easy Ringtones

Create iPhone ringtones the way you want them to sound. Drag the clip handles to set a repeating snippet from a song, control fade in and fade outs, and set a gap between loops.

Works with iTunes

Ringtones is a great companion to iTunes. Make iPhone ringtones from any DRM-free song in your music library, and then export it back to iTunes to sync with your iPhone.