Rogue Amoeba CEO Paul Kafasis:
Today, we’re releasing Fission 2.4 with revamped ringtone saving. Using Fission, you can once again save custom tones for use on your iOS device. While the new iTunes makes it much less obvious, it is indeed still possible to load custom tones onto your iOS device, right from your Mac.
Not only does Fission let you make custom ringtones, they’ve got step-by-step instructions for getting them on your iOS device.
An interesting side note: Kafasis points out that GarageBand’s own ringtone-export feature has been broken by the changes to iTunes.